blocks|key|390386|text|使用此代码|type|unstyled|depth|inlineStyleRanges|entityRanges|data|390387|+@Override
+public+void+onCreate(Bundle+savedInstanceState)+{
++++...
+++getActionBar().setDisplayHomeAsUpEnabled(true);
+}+|code-block|syntax|javascript|390388|之后，在onOptionsItemSelected方法中编写以下代码|offset|length|style|CODE|390389|++int+id+=+item.getItemId();

+++++if+(id==android.R.id.home)+{
++++++++finish();
++++}|390390|entityMap^0|0|0|4|L|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

use this code 

<pre><code> @Override
 public void onCreate(Bundle savedInstanceState) {
 ...
 getActionBar().setDisplayHomeAsUpEnabled(true);
 } 
</code></pre>

after that write this code in <code>onOptionsItemSelected</code> method

<pre><code> int id = item.getItemId();

 if (id==android.R.id.home) {
 finish();
 }
</code></pre>

blocks|key|172359|text|我终于成功地将后退按钮正确地添加到actionbar/工具栏|type|unstyled|depth|inlineStyleRanges|entityRanges|data|172360|@Override
public+void+onCreate(Bundle+savedInstanceState)+{
++++...
++++getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}++

@Override
public+boolean+onOptionsItemSelected(MenuItem+item)+{
++++switch+(item.getItemId())+{
++++++++case+android.R.id.home:
++++++++++++finish();
++++++++++++return+true;
++++}

++++return+super.onOptionsItemSelected(item);
}

public+boolean+onCreateOptionsMenu(Menu+menu)+{
++++return+true;
}|code-block|syntax|javascript|172361|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I have finally managed to properly add back button to actionbar/toolbar

<pre><code>@Override
public void onCreate(Bundle savedInstanceState) {
 ...
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
} 

@Override
public boolean onOptionsItemSelected(MenuItem item) {
 switch (item.getItemId()) {
 case android.R.id.home:
 finish();
 return true;
 }

 return super.onOptionsItemSelected(item);
}

public boolean onCreateOptionsMenu(Menu menu) {
 return true;
}
</code></pre>

blocks|key|390757|text|首先，在onCreate函数中添加以下行|type|unstyled|depth|inlineStyleRanges|entityRanges|data|390758|getSupportActionBar().setDisplayHomeAsUpEnabled(true);|code-block|syntax|javascript|390759|然后在代码中添加以下函数：|390760|@Override
++++public+boolean+onOptionsItemSelected(MenuItem+item)+{
++++++++switch+(item.getItemId())+{
++++++++++++case+android.R.id.home:
++++++++++++++++finish();
++++++++++++++++return+true;
++++++++}

++++++++return+super.onOptionsItemSelected(item);
++++}|390761|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

first of all in onCreate Function add the following line

<pre><code>getSupportActionBar().setDisplayHomeAsUpEnabled(true);
</code></pre>

and then add the following function in the code:

<pre><code>@Override
 public boolean onOptionsItemSelected(MenuItem item) {
 switch (item.getItemId()) {
 case android.R.id.home:
 finish();
 return true;
 }

 return super.onOptionsItemSelected(item);
 }
</code></pre>

blocks|key|172625|text|如果您的活动扩展了AppCompatActivity，则需要覆盖onSupportNavigateUp()方法，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|172626|public+class+SecondActivity+extends+AppCompatActivity+{

+++@Override
+++protected+void+onCreate(Bundle+savedInstanceState)+{
+++++++super.onCreate(savedInstanceState);
+++++++setContentView(R.layout.activity_second);
+++++++Toolbar+toolbar+=+(Toolbar)+findViewById(R.id.toolbar);
+++++++setSupportActionBar(toolbar);
+++++++getSupportActionBar().setHomeButtonEnabled(true);
+++++++getSupportActionBar().setDisplayHomeAsUpEnabled(true);
+++++++...
+++}

+++@Override
+++public+void+onBackPressed()+{
+++++++super.onBackPressed();
+++++++this.finish();
+++}

+++@Override
+++public+boolean+onSupportNavigateUp()+{
+++++++onBackPressed();
+++++++return+true;
+++}
}|code-block|syntax|javascript|172627|在onBackPressed()方法中处理您的逻辑，并在onSupportNavigateUp()中调用该方法，这样电话上的后退按钮和工具栏上的箭头就可以做同样的事情。|172628|entityMap^0|9|H|W|L|0|0|1|F|S|L|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|N|$]]

If your activity extends <code>AppCompatActivity</code> you need to override the <code>onSupportNavigateUp()</code> method like so:

<pre><code>public class SecondActivity extends AppCompatActivity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_second);
 Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
 setSupportActionBar(toolbar);
 getSupportActionBar().setHomeButtonEnabled(true);
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
 ...
 }

 @Override
 public void onBackPressed() {
 super.onBackPressed();
 this.finish();
 }

 @Override
 public boolean onSupportNavigateUp() {
 onBackPressed();
 return true;
 }
}
</code></pre>

Handle your logic in your <code>onBackPressed()</code> method and just call that method in <code>onSupportNavigateUp()</code> so the back button on the phone and the arrow on the toolbar do the same thing.

blocks|key|172949|text|经过一段时间后，我发现主题选项是我的代码中的主要问题，下面是为我显示工具栏的正确方式|type|unstyled|depth|inlineStyleRanges|entityRanges|data|172950|在AndroidManifest文件中，首先你必须改变你的主题风格|172951|Theme.AppCompat.Light.DarkActionBar
to+
Theme.AppCompat.Light.NoActionBar|code-block|syntax|javascript|172952|然后，在您的活动xml中，您需要调用您自己的工具栏，如下所示|172953|<androidx.appcompat.widget.Toolbar
++++++++android:layout_width="match_parent"
++++++++android:layout_height="?attr/actionBarSize"
++++++++android:background="@color/colorPrimary"
++++++++android:id="@%2Bid/toolbar"
++++++++android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
++++++++android:elevation="4dp"/>|172954|然后，在您的Java文件中应该通过以下方式调用此工具栏|172955|Toolbar+toolbar+=+findViewById(R.id.toolbar);
setSupportActionBar(toolbar);|172956|对于显示U的工具栏，应检查null以避免NullPointerException|172957|if(getSupportActionBar()+!=+null){
++++getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}|172958|对于Home+activity+back，添加以下内容|172959|@Override
public+boolean+onOptionsItemSelected(MenuItem+item)+{
++++++++if+(item.getItemId()==android.R.id.home)+{
++++++++++++finish();
++++++++++++return+true;
++++++++}

++++++++return+super.onOptionsItemSelected(item);
++++}|172960|或者为了你想要的活动回来|172961|public+boolean+onOptionsItemSelected(MenuItem+item){
++++Intent+myIntent+=+new+Intent(getApplicationContext(),+YourActivity.class);
++++startActivityForResult(myIntent,+0);
++++return+true;
}|172962|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|15|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|17|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|18|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|19|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1B|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|1D|8|@]|9|@]|A|$]]|$1|W|3|X|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|Y|3|Z|5|6|7|1F|8|@]|9|@]|A|$]]|$1|10|3|11|5|F|7|1G|8|@]|9|@]|A|$G|H]]|$1|12|3|-4|5|6|7|1H|8|@]|9|@]|A|$]]]|13|$]]

After a quality time I have found, theme option is the main problem in my code And following is the proper way to show the toolbar for me

In AndroidManifest file first you have to change your theme style 

<pre><code>Theme.AppCompat.Light.DarkActionBar
to 
Theme.AppCompat.Light.NoActionBar
</code></pre>

then at your activity xml you need to call your own Toolbar like 

<pre><code>&lt;androidx.appcompat.widget.Toolbar
 android:layout_width="match_parent"
 android:layout_height="?attr/actionBarSize"
 android:background="@color/colorPrimary"
 android:id="@+id/toolbar"
 android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
 android:elevation="4dp"/&gt;
</code></pre>

And then this toolbar should be called in your Java file by 

<pre><code>Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
</code></pre>

And for toolbar showing U should check the null to avoid NullPointerException

<pre><code>if(getSupportActionBar() != null){
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
</code></pre>

For Home activity back add this 

<pre><code>@Override
public boolean onOptionsItemSelected(MenuItem item) {
 if (item.getItemId()==android.R.id.home) {
 finish();
 return true;
 }

 return super.onOptionsItemSelected(item);
 }
</code></pre>

OR for your desired activity back

<pre><code>public boolean onOptionsItemSelected(MenuItem item){
 Intent myIntent = new Intent(getApplicationContext(), YourActivity.class);
 startActivityForResult(myIntent, 0);
 return true;
}
</code></pre>

blocks|key|172484|text|如果你在android+studio中使用新的5.1支持库，你可以在你的AppCompatActivity上使用它|type|unstyled|depth|inlineStyleRanges|entityRanges|data|172485|+ActionBar+actionBar+=+getSupportActionBar();
+actionBar.setHomeButtonEnabled(true);
+actionBar.setDisplayHomeAsUpEnabled(true);
+actionBar.setHomeAsUpIndicator(R.mipmap.ic_arrow_back_white_24dp);
+actionBar.setDisplayShowHomeEnabled(true);|code-block|syntax|javascript|172486|干杯。|172487|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you are using the new support library for 5.1 in android studio, you can instead use this on your AppCompatActivity

<pre><code> ActionBar actionBar = getSupportActionBar();
 actionBar.setHomeButtonEnabled(true);
 actionBar.setDisplayHomeAsUpEnabled(true);
 actionBar.setHomeAsUpIndicator(R.mipmap.ic_arrow_back_white_24dp);
 actionBar.setDisplayShowHomeEnabled(true);
</code></pre>

cheers.

blocks|key|390561|text|谷歌解释in+here的最简单的方法和最佳实践：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|390562|1.在AndroidManifest.xml中为您的childActivity添加父级：|style|CODE|390563|<activity+
++++++++android:name=".ChildActivity"
++++++++android:parentActivityName=".ParentActivity"+>
</activity>|code-block|syntax|javascript|390564|2.激活childActivity中的后退按钮：|390565|myActionOrActionSupportBar.setDisplayHomeAsUpEnabled(true);|390566|对我有效，我希望对你也有效。|390567|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.android.com/training/implementing-navigation/ancestral.html^0|4|7|0|0|3|J|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@$A|15|B|16|F|G]]|9|@]|C|$]]|$1|H|3|I|5|J|7|17|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|18|8|@]|9|@]|C|$]]|$1|O|3|P|5|J|7|19|8|@]|9|@]|C|$K|L]]|$1|Q|3|R|5|6|7|1A|8|@]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

The simplest way and best practice as google explains <a href="https://developer.android.com/training/implementing-navigation/ancestral.html" rel="noreferrer" title="developer.android.com">in here</a> :

1.Add a parent for your childActivity in the <code>AndroidManifest.xml</code> :

<pre><code>&lt;activity 
 android:name=".ChildActivity"
 android:parentActivityName=".ParentActivity" &gt;
&lt;/activity&gt;
</code></pre>

2.Activate the back button in your childActivity :

<pre><code>myActionOrActionSupportBar.setDisplayHomeAsUpEnabled(true);
</code></pre>

Worked for me, I hope it works for you too.

blocks|key|390938|text|++protected+void+onCreate(Bundle+savedInstanceState)+{
++++++++super.onCreate(savedInstanceState);
++++++++setContentView(R.layout.YourxmlFileName);
++++++++getSupportActionBar().setDisplayHomeAsUpEnabled(true);
++++}

++public+boolean+onOptionsItemSelected(MenuItem+item)+{
++++++++int+id+=+item.getItemId();

++++++++if+(id==android.R.id.home)+{
++++++++++++finish();
++++++++++++return+true;
++++++++}
++++++++return+false;
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|390939|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code> protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.YourxmlFileName);
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
 }

 public boolean onOptionsItemSelected(MenuItem item) {
 int id = item.getItemId();

 if (id==android.R.id.home) {
 finish();
 return true;
 }
 return false;
 }
</code></pre>

blocks|key|390892|text|我看到了很多复杂的答案，所以这是我的代码。在这里工作。您可以通过两种方式来实现这一点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|390893|1)标准android兼容性|390894|import+androidx.appcompat.app.AppCompatActivity;
import+androidx.appcompat.widget.Toolbar;
import+androidx.core.app.NavUtils;

import+android.view.MenuItem;
import+android.view.View;

public+class+EditDiscoveryActivity+extends+AppCompatActivity+{

++++@Override
++++protected+void+onCreate(Bundle+savedInstanceState)+{
++++++++super.onCreate(savedInstanceState);
++++++++setContentView(R.layout.activity_edit_discovery);
++++++++Toolbar+toolbar+=+findViewById(R.id.toolbar);
++++++++setSupportActionBar(toolbar);

++++++++/*toolbar.setNavigationIcon(R.drawable.ic_arrow_white_24dp);
++++++++toolbar.setNavigationOnClickListener(new+View.OnClickListener()+{
++++++++++++@Override
++++++++++++public+void+onClick(View+view)+{
++++++++++++++++finish();
++++++++++++}
++++++++});*/
++++++++getSupportActionBar().setDisplayHomeAsUpEnabled(true);
++++++++getSupportActionBar().setDisplayShowHomeEnabled(true);
++++}

++++@Override
++++public+boolean+onSupportNavigateUp()+{
++++++++onBackPressed();
++++++++return+true;
++++}

}|code-block|syntax|javascript|390895|2)使用自定义图标|390896|如果您想在注释中使用代码，只需在可绘制的文件中添加名为ic_arrow_white_24dp.xml的文件|390897|<vector+xmlns:android="http://schemas.android.com/apk/res/android"
++++android:width="24dp"
++++android:height="24dp"
++++android:viewportWidth="24.0"
++++android:viewportHeight="24.0">
++++<path
++++++++android:fillColor="#ffffff"
++++++++android:pathData="M20,11H7.83l5.59,-5.59L12,4l-8,8+8,8+1.41,-1.41L7.83,13H20v-2z"/>
++++</vector>|390898|使用此代码。|390899|toolbar.setNavigationIcon(R.drawable.ic_arrow_white_24dp);
++++++++++++toolbar.setNavigationOnClickListener(new+View.OnClickListener()+{
++++++++++++++++@Override
++++++++++++++++public+void+onClick(View+view)+{
++++++++++++++++++++finish();
++++++++++++++++}
++++++++++++});|390900|希望能对这里的一些人有所帮助！|390901|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|11|8|@]|9|@]|A|$G|H]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|13|8|@]|9|@]|A|$G|H]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

I saw so much complexes answer, so this is my code. Working here. You can achieve this in two ways.

1) Stardard android compatiblity

<pre><code>import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.core.app.NavUtils;

import android.view.MenuItem;
import android.view.View;

public class EditDiscoveryActivity extends AppCompatActivity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_edit_discovery);
 Toolbar toolbar = findViewById(R.id.toolbar);
 setSupportActionBar(toolbar);

 /*toolbar.setNavigationIcon(R.drawable.ic_arrow_white_24dp);
 toolbar.setNavigationOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View view) {
 finish();
 }
 });*/
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
 getSupportActionBar().setDisplayShowHomeEnabled(true);
 }

 @Override
 public boolean onSupportNavigateUp() {
 onBackPressed();
 return true;
 }

}
</code></pre>

2) Use a custom icon

If you want to use code in comments you just have to add this file in drawable, called ic_arrow_white_24dp.xml

<pre><code>&lt;vector xmlns:android="http://schemas.android.com/apk/res/android"
 android:width="24dp"
 android:height="24dp"
 android:viewportWidth="24.0"
 android:viewportHeight="24.0"&gt;
 &lt;path
 android:fillColor="#ffffff"
 android:pathData="M20,11H7.83l5.59,-5.59L12,4l-8,8 8,8 1.41,-1.41L7.83,13H20v-2z"/&gt;
 &lt;/vector&gt;
</code></pre>

With this code.

<pre><code>toolbar.setNavigationIcon(R.drawable.ic_arrow_white_24dp);
 toolbar.setNavigationOnClickListener(new View.OnClickListener() {
 @Override
 public void onClick(View view) {
 finish();
 }
 });
</code></pre>

Hope it will helps some people here !

blocks|key|172425|text|没有使用ActionBarActivity的轻量级版本，仍然具有相同的行为：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|172426|public+class+ToolbarConfigurer+implements+View.OnClickListener+{
++++private+Activity+activity;

++++public+ToolbarConfigurer(Activity+activity,+Toolbar+toolbar,+boolean+displayHomeAsUpEnabled)+{
++++++++toolbar.setTitle((this.activity+=+activity).getTitle());
++++++++if+(!displayHomeAsUpEnabled)+return;
++++++++toolbar.setNavigationIcon(R.drawable.abc_ic_ab_back_mtrl_am_alpha);
++++++++toolbar.setNavigationOnClickListener(this);
++++}

++++@Override
++++public+void+onClick(View+v)+{
++++++++NavUtils.navigateUpFromSameTask(activity);
++++}
}|code-block|syntax|javascript|172427|用法:将new+ToolbarConfigurer(this,+(Toolbar)+findViewById(R.id.my_awesome_toolbar),+true);放入onCreate。|172428|entityMap^0|4|H|0|0|4|2B|2H|8|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

Light-weighted version without using <code>ActionBarActivity</code> that still has the same bahaviors here:

<pre><code>public class ToolbarConfigurer implements View.OnClickListener {
 private Activity activity;

 public ToolbarConfigurer(Activity activity, Toolbar toolbar, boolean displayHomeAsUpEnabled) {
 toolbar.setTitle((this.activity = activity).getTitle());
 if (!displayHomeAsUpEnabled) return;
 toolbar.setNavigationIcon(R.drawable.abc_ic_ab_back_mtrl_am_alpha);
 toolbar.setNavigationOnClickListener(this);
 }

 @Override
 public void onClick(View v) {
 NavUtils.navigateUpFromSameTask(activity);
 }
}
</code></pre>

Usage: Put <code>new ToolbarConfigurer(this, (Toolbar) findViewById(R.id.my_awesome_toolbar), true);</code> in <code>onCreate</code>.

blocks|key|390596|text|您需要在清单文件中添加下面提到的代码。搜索要在其中添加向后箭头功能的活动。如果您找到了合适的活动，则可以创建该活动|type|unstyled|depth|inlineStyleRanges|entityRanges|data|390597|<activity+android:name=".SearchActivity">

</activity>|code-block|syntax|javascript|390598|然后在中间添加以下三行代码。|390599|<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.example.raqib.instadate.MainActivity"+/>|390600|不要忘了将这段代码添加到您需要返回箭头的特定活动的onCreate()；方法中。|390601|++++++++Toolbar+toolbar+=+(Toolbar)+findViewById(R.id.searchToolbar);
++++setSupportActionBar(toolbar);
++++try{
++++++++getSupportActionBar().setDisplayHomeAsUpEnabled(true);
++++}catch(NullPointerException+e){
+++++++Log.e("SearchActivity+Toolbar",+"You+have+got+a+NULL+POINTER+EXCEPTION");
++++}|390602|这就是我解决问题的方法。谢谢。|390603|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

You need to add the below mentioned code in the manifest file.
Search for the activity in which you want to add the back arrow functionality.
If you find the one then fine or create the activity 

<pre><code>&lt;activity android:name=".SearchActivity"&gt;

&lt;/activity&gt;
</code></pre>

Then add the following three lines of code in between.

<pre><code>&lt;meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.example.raqib.instadate.MainActivity" /&gt;
</code></pre>

And don't forget to add this piece of code in onCreate(); method of your particular activity in which you need back arrow.

<pre><code> Toolbar toolbar = (Toolbar) findViewById(R.id.searchToolbar);
 setSupportActionBar(toolbar);
 try{
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
 }catch(NullPointerException e){
 Log.e("SearchActivity Toolbar", "You have got a NULL POINTER EXCEPTION");
 }
</code></pre>

This is how i solved the problem.
Thanks.

blocks|key|390795|text|对于kotlin：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|390796|+++override+fun+onOptionsItemSelected(item:+MenuItem):+Boolean+{
++++++++onBackPressed();
++++++++return+true;
++++}|code-block|syntax|javascript|390797|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For kotlin :

<pre><code> override fun onOptionsItemSelected(item: MenuItem): Boolean {
 onBackPressed();
 return true;
 }
</code></pre>

blocks|key|172794|text|我需要混合一些答案才能得到正确的答案，因为我的应用程序有3个可以随时往返的活动。Activity1+>+Activity2+>+Activity3。当我在我的activity3上做一些事情时，后退按钮正确地回到了Activity2上。然而，从Activity2，使用finish()，它返回到Activity3，而不是Activity1。我正在扩展AppCompatActivity。所以，我的解决方案是：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|172795|public+class+Activity2+extends+AppCompatActivity+{
++++++++@Override
++++++++protected+void+onCreate(Bundle+savedInstanceState)+{
++++++++++++...

++++++++++++getSupportActionBar().setHomeButtonEnabled(true);
++++++++}
++++}|code-block|syntax|javascript|172796|在AndroidManifest.xml上：|172797|<activity+android:name=".activities.Activity2"
+++++++++++android:parentActivityName="com.example.appname.activities.Activity1">
++++++++++++<meta-data
++++++++++++++++android:name="android.support.PARENT_ACTIVITY"
++++++++++++++++android:value="com.example.appname.activities.Activity1"+/>
++++++++</activity>|172798|最后，我的菜单上的操作按钮(actionbar)：|172799|public+boolean+onOptionsItemSelected(MenuItem+item)+{
++++++++switch+(item.getItemId()){
++++++++++++...

++++++++++++case+android.R.id.home:
++++++++++++++++NavUtils.navigateUpFromSameTask(this);
++++++++++++++++return+true;

++++++++}

++++++++return+super.onOptionsItemSelected(item);

++++}|172800|在我看来，使用NavUtils.navigateUpFromSameTask(this);而不是finish()是可行的。|172801|entityMap^0|3P|8|0|0|0|0|0|0|7|12|1C|8|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|11|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|12|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|S|3|T|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|U|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|V|$]]

I needed to mix some answers to get the right answer for me because my app has 3 activities that can go and back at any time. Activity1 > Activity2 > Activity3. When I was doing something on my activity3, the back button was backing correctly to Activity2. However, from the Activity2, using <code>finish()</code>, it was backing to Activity3 and not Activity1. And I'm extending AppCompatActivity. So, my solution was:

<pre><code>public class Activity2 extends AppCompatActivity {
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 ...

 getSupportActionBar().setHomeButtonEnabled(true);
 }
 }
</code></pre>

on AndroidManifest.xml:

<pre><code>&lt;activity android:name=".activities.Activity2"
 android:parentActivityName="com.example.appname.activities.Activity1"&gt;
 &lt;meta-data
 android:name="android.support.PARENT_ACTIVITY"
 android:value="com.example.appname.activities.Activity1" /&gt;
 &lt;/activity&gt;
</code></pre>

and finally, the action button on my menu (actionbar):

<pre><code>public boolean onOptionsItemSelected(MenuItem item) {
 switch (item.getItemId()){
 ...

 case android.R.id.home:
 NavUtils.navigateUpFromSameTask(this);
 return true;

 }

 return super.onOptionsItemSelected(item);

 }
</code></pre>

Using <code>NavUtils.navigateUpFromSameTask(this);</code> worked for me, instead of <code>finish()</code>.

blocks|key|172828|text|其他答案没有提到您也可以在Toolbar小部件的XML中设置：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|172829|app:navigationIcon="?attr/homeAsUpIndicator"|172830|例如：|172831|<android.support.v7.widget.Toolbar
++++android:id="@%2Bid/toolbar"
++++android:layout_width="match_parent"
++++android:layout_height="?attr/actionBarSize"
++++android:background="?attr/colorPrimary"
++++app:navigationIcon="?attr/homeAsUpIndicator"
++++app:popupTheme="@style/AppTheme.PopupOverlay"
++++app:title="@string/title_activity_acoustic_progress"+/>|code-block|syntax|javascript|172832|entityMap^0|D|7|0|0|18|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|W|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|X|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

The other answers don't mention that you can also set this in the XML of your <code>Toolbar</code> widget:

<code>app:navigationIcon="?attr/homeAsUpIndicator"</code>

For example:

<pre><code>&lt;android.support.v7.widget.Toolbar
 android:id="@+id/toolbar"
 android:layout_width="match_parent"
 android:layout_height="?attr/actionBarSize"
 android:background="?attr/colorPrimary"
 app:navigationIcon="?attr/homeAsUpIndicator"
 app:popupTheme="@style/AppTheme.PopupOverlay"
 app:title="@string/title_activity_acoustic_progress" /&gt;
</code></pre>

blocks|key|172863|text|只是分享一些对我有帮助，也可能对其他人有用的东西。虽然这里的大多数答案都是正确的，但通过使用getActionBar().setDisplayHomeAsUpEnabled(true);，这对我来说不起作用。我遇到的问题是，我试图手动创建第二个活动，但涉及到更多细节。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|172864|真正解决了我的问题的是遵循Android开发人员教程(https://developer.android.com/training/basics/firstapp/starting-activity)，使用Android+Studio自己的工具创建第二个活动：|172865|Create+the+second+activity
1.+In+the+Project+window,+right-click+the+app+folder+and+select+New+>+Activity+>+Empty+Activity.
2.+In+the+Configure+Activity+window,+enter+"DisplayMessageActivity"+for+Activity+Name+and+click+Finish+(leave+all+other+properties+set+to+the+defaults).
Android+Studio+automatically+does+three+things:
-+Creates+the+DisplayMessageActivity+file.
-+Creates+the+corresponding+activity_display_message.xml+layout+file.
-+Adds+the+required+<activity>+element+in+AndroidManifest.xml.|code-block|syntax|javascript|172866|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.android.com/training/basics/firstapp/starting-activity^0|1A|1B|0|R|20|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|X|8|@]|D|@$9|Y|A|Z|1|10]]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

Just sharing something that helped me and may be useful for others. Although most of the answers here are correct, by using the <code>getActionBar().setDisplayHomeAsUpEnabled(true);</code>, this wasn't working for me. The issue I had was that I was trying to create a second Activity manually, but there are more details involved. 
What really solved my problem was following Android Developers tutorial (<a href="https://developer.android.com/training/basics/firstapp/starting-activity" rel="nofollow noreferrer">https://developer.android.com/training/basics/firstapp/starting-activity</a>) for creating a second Activity using Android Studio own tools:

<pre><code>Create the second activity
1. In the Project window, right-click the app folder and select New &gt; Activity &gt; Empty Activity.
2. In the Configure Activity window, enter "DisplayMessageActivity" for Activity Name and click Finish (leave all other properties set to the defaults).
Android Studio automatically does three things:
- Creates the DisplayMessageActivity file.
- Creates the corresponding activity_display_message.xml layout file.
- Adds the required &lt;activity&gt; element in AndroidManifest.xml.
</code></pre>

blocks|key|390362|text|如果您使用的是ActionBar，则需要阅读本文档http://developer.android.com/reference/android/app/ActionBar.html#setDisplayHomeAsUpEnabled(boolean)|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|390363|然后，您必须重写方法onOptionsItemSelected(MenuItem)并查找要传入的android.R.id.home事件。然后，您就知道用户已经单击了操作栏上的后退按钮|390364|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.android.com/reference/android/app/ActionBar.html#setDisplayHomeAsUpEnabled(boolean)^0|P|2S|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

If you are using an ActionBar you're going to want to read up on this documentation 
<a href="http://developer.android.com/reference/android/app/ActionBar.html#setDisplayHomeAsUpEnabled(boolean)" rel="nofollow">http://developer.android.com/reference/android/app/ActionBar.html#setDisplayHomeAsUpEnabled(boolean)</a>

Then you have to overwrite the method onOptionsItemSelected(MenuItem) and look for the android.R.id.home event to come in. Then you know the user has clicked on that back button on the actionbar

blocks|key|390738|text|也可以在没有代码的情况下通过在应用程序清单中指定父活动来完成此操作。如果您希望在活动B中有一个返回按钮，则只需在清单中将活动A添加为活动B的父活动即可。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|390739|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It can also be done without code by specifying a parent activity in app manifest 
If you want a back button in Activity B which will goto Activity A, just add Activity A as the parent of Activity B in the manifest.

blocks|key|172455|text|您也可以简单地将onBackPressed()放在onClick侦听器中。这使得你的按钮就像android应用程序中默认的“后退/上一步”按钮！|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|172456|entityMap^0|8|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

You can also simply put <code>onBackPressed()</code> in your onClick listener. This causes your button to act like the default "back/up" buttons in android apps!

blocks|key|390767|text|Toolbar+toolbar=findViewById(R.id.toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);

if+(getSupportActionBar()==null){
++++getSupportActionBar().setDisplayHomeAsUpEnabled(true);
++++getSupportActionBar().setDisplayShowHomeEnabled(true);
}

@Override
public+boolean+onOptionsItemSelected(MenuItem+item)+{
if(item.getItemId()==android.R.id.home)
++++finish();
return+super.onOptionsItemSelected(item);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|390768|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>Toolbar toolbar=findViewById(R.id.toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);

if (getSupportActionBar()==null){
 getSupportActionBar().setDisplayHomeAsUpEnabled(true);
 getSupportActionBar().setDisplayShowHomeEnabled(true);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
if(item.getItemId()==android.R.id.home)
 finish();
return super.onOptionsItemSelected(item);
}
</code></pre>

blocks|key|172746|text|这对我很有效，getSupportActionBar().setDisplayHomeAsUpEnabled(false)；enter+image+description+here|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|172747|entityMap|0|LINK|mutability|MUTABLE|url|https://i.stack.imgur.com/J3zZ6.png^0|1Q|S|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

This is working for me
getSupportActionBar().setDisplayHomeAsUpEnabled(false);
<a href="https://i.stack.imgur.com/J3zZ6.png" rel="nofollow noreferrer">enter image description here</a>

In many apps (Calendar, Drive, Play Store) when you tap a button and enter a new activity, the icon in the title bar turns into a back button, but for the app I am making, it doesn't do that. How do I make that icon take you back to the previous screen?

Android - Back button in the title bar

Android Studio

Android

Java

在许多应用程序(日历、驱动器、Play Store)中，当你点击一个按钮并进入一个新的活动时，标题栏中的图标会变成一个后退按钮，但对于我正在制作的应用程序，它不会这样做。如何使该图标返回到上一个屏幕？

问Android -标题栏中的后退按钮
EN

回答 20

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Android -标题栏中的后退按钮EN

回答 20

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Android -标题栏中的后退按钮
EN