blocks|key|1218465|text|为什么、如何以及哪些参数传递给Asynctask<>，请参见详细的here。我认为这是最好的解释。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1218466|谷歌的Android文档中写道：|1218467|异步任务由3个通用类型定义，分别称为参数、进度和结果，以及4个步骤，分别称为onPreExecute、doInBackground、onProgressUpdate和onPostExecute。|1218468|AsyncTask的泛型类型：|1218469|异步任务使用的三种类型如下：|1218470|Params，执行时发送给任务的参数类型。进度，后台计算过程中发布的进度单位的类型。结果，后台计算的结果的类型。并非所有类型都总是由异步任务使用。要将类型标记为未使用，只需使用类型Void：|1218471|+private+class+MyTask+extends+AsyncTask<Void,+Void,+Void>+{+...+}|code-block|syntax|javascript|1218472|你可以进一步参考：http://developer.android.com/reference/android/os/AsyncTask.html|1218473|或者你可以通过参考Sankar-Ganesh的博客来明确AsyncTask的作用|1218474|一个典型的AsyncTask类的结构如下：|1218475|private+class+MyTask+extends+AsyncTask<X,+Y,+Z>

++++protected+void+onPreExecute(){+

++++}+|1218476|此方法在启动新的Thread之前执行。没有输入/输出值，所以只需初始化变量或您认为需要做的任何事情。|1218477|protected+Z+doInBackground(X...x){

}|1218478|AsyncTask类中最重要的方法。你必须把所有你想要做的事情放在后台，放在不同于主线程的线程中。这里我们有一个“X”类型的对象数组作为输入值(您在标题中看到了吗？我们有“...extends+AsyncTask”，这些是输入参数的类型)，并从类型“Z”返回一个对象。|1218479|protected+void+onProgressUpdate(Y+y){|1218480|}此方法使用方法publishProgress(y)调用，通常在您想要在主屏幕中显示任何进度或信息时使用，如在后台显示操作进度的进度条。|1218481|protected+void+onPostExecute(Z+z){|1218482|}此方法在后台操作完成后调用。作为输入参数，您将收到doInBackground方法的输出参数。|1218483|那么X、Y和Z类型呢？|1218484|从上面的结构可以推断出：|1218485|X+–+The+type+of+the+input+variables+value+you+want+to+set+to+the+background+process.+This+can+be+an+array+of+objects.

+Y+–+The+type+of+the+objects+you+are+going+to+enter+in+the+onProgressUpdate+method.

+Z+–+The+type+of+the+result+from+the+operations+you+have+done+in+the+background+process.|1218486|如何从外部类调用此任务？只有以下两行：|1218487|MyTask+myTask+=+new+MyTask();

myTask.execute(x);|1218488|其中X是类型X的输入参数。|1218489|一旦我们的任务运行起来，我们就可以从“外部”找到它的状态。使用“getStatus()”方法。|1218490|myTask.getStatus()；，我们可以收到以下状态：|1218491|正在运行-表示任务正在运行。|1218492|挂起-表示任务尚未执行。|1218493|已完成-指示onPostExecute(Z)已完成。|1218494|关于使用AsyncTask的提示|1218495|请勿手动调用onPreExecute、doInBackground和onPostExecute方法。这是由系统自动完成的。|1218496|不能在另一个AsyncTask或线程内部调用AsyncTask。方法execute的调用必须在UI线程中完成。|1218497|方法onPostExecute在UI中执行(在这里您可以调用另一个AsyncTask!)。|1218498|任务的输入参数可以是一个对象数组，这样你就可以放置任何你想要的对象和类型。|1218499|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/6053602/what-arguments-are-passed-into-asynctaskarg1-arg2-arg3|1|http://developer.android.com/reference/android/os/AsyncTask.html^0|X|4|0|0|0|0|0|0|0|0|9|1S|1|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|2K|8|@]|9|@$A|2L|B|2M|1|2N]]|C|$]]|$1|D|3|E|5|6|7|2O|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|2P|8|@]|9|@]|C|$]]|$1|H|3|I|5|6|7|2Q|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|2R|8|@]|9|@]|C|$]]|$1|L|3|M|5|6|7|2S|8|@]|9|@]|C|$]]|$1|N|3|O|5|P|7|2T|8|@]|9|@]|C|$Q|R]]|$1|S|3|T|5|6|7|2U|8|@]|9|@$A|2V|B|2W|1|2X]]|C|$]]|$1|U|3|V|5|6|7|2Y|8|@]|9|@]|C|$]]|$1|W|3|X|5|6|7|2Z|8|@]|9|@]|C|$]]|$1|Y|3|Z|5|P|7|30|8|@]|9|@]|C|$Q|R]]|$1|10|3|11|5|6|7|31|8|@]|9|@]|C|$]]|$1|12|3|13|5|P|7|32|8|@]|9|@]|C|$Q|R]]|$1|14|3|15|5|6|7|33|8|@]|9|@]|C|$]]|$1|16|3|17|5|6|7|34|8|@]|9|@]|C|$]]|$1|18|3|19|5|6|7|35|8|@]|9|@]|C|$]]|$1|1A|3|1B|5|6|7|36|8|@]|9|@]|C|$]]|$1|1C|3|1D|5|6|7|37|8|@]|9|@]|C|$]]|$1|1E|3|1F|5|6|7|38|8|@]|9|@]|C|$]]|$1|1G|3|1H|5|6|7|39|8|@]|9|@]|C|$]]|$1|1I|3|1J|5|P|7|3A|8|@]|9|@]|C|$Q|R]]|$1|1K|3|1L|5|6|7|3B|8|@]|9|@]|C|$]]|$1|1M|3|1N|5|P|7|3C|8|@]|9|@]|C|$Q|R]]|$1|1O|3|1P|5|6|7|3D|8|@]|9|@]|C|$]]|$1|1Q|3|1R|5|6|7|3E|8|@]|9|@]|C|$]]|$1|1S|3|1T|5|6|7|3F|8|@]|9|@]|C|$]]|$1|1U|3|1V|5|6|7|3G|8|@]|9|@]|C|$]]|$1|1W|3|1X|5|6|7|3H|8|@]|9|@]|C|$]]|$1|1Y|3|1Z|5|6|7|3I|8|@]|9|@]|C|$]]|$1|20|3|21|5|6|7|3J|8|@]|9|@]|C|$]]|$1|22|3|23|5|6|7|3K|8|@]|9|@]|C|$]]|$1|24|3|25|5|6|7|3L|8|@]|9|@]|C|$]]|$1|26|3|27|5|6|7|3M|8|@]|9|@]|C|$]]|$1|28|3|29|5|6|7|3N|8|@]|9|@]|C|$]]|$1|2A|3|-4|5|6|7|3O|8|@]|9|@]|C|$]]]|2B|$2C|$5|2D|2E|2F|C|$2G|2H]]|2I|$5|2D|2E|2F|C|$2G|2J]]]]

why, how and which parameters are passed to Asynctask&lt;>, see detail <a href="https://stackoverflow.com/questions/6053602/what-arguments-are-passed-into-asynctaskarg1-arg2-arg3">here</a>. I think it is the best explanation.

Google's Android Documentation Says that :

An asynchronous task is defined by 3 generic types, called Params, Progress and Result, and 4 steps, called onPreExecute, doInBackground, onProgressUpdate and onPostExecute.

AsyncTask's generic types :

The three types used by an asynchronous task are the following:

Params, the type of the parameters sent to the task upon execution.
Progress, the type of the progress units published during the background computation.
Result, the type of the result of the background computation.
Not all types are always used by an asynchronous task. To mark a type as unused, simply use the type Void:

<pre><code> private class MyTask extends AsyncTask&lt;Void, Void, Void&gt; { ... }
</code></pre>

You Can further refer : <a href="http://developer.android.com/reference/android/os/AsyncTask.html" rel="nofollow noreferrer">http://developer.android.com/reference/android/os/AsyncTask.html</a>

Or You Can clear whats the role of AsyncTask by refering Sankar-Ganesh's Blog

Well The structure of a typical AsyncTask class goes like :

<pre><code>private class MyTask extends AsyncTask&lt;X, Y, Z&gt;

 protected void onPreExecute(){ 

 } 
</code></pre>

This method is executed before starting the new Thread. There is no input/output values, so just initialize variables or whatever you think you need to do.

<pre><code>protected Z doInBackground(X...x){

}
</code></pre>

The most important method in the AsyncTask class. You have to place here all the stuff you want to do in the background, in a different thread from the main one. Here we have as an input value an array of objects from the type “X” (Do you see in the header? We have “...extends AsyncTask” These are the TYPES of the input parameters) and returns an object from the type “Z”.

protected void onProgressUpdate(Y y){

}
This method is called using the method publishProgress(y) and it is usually used when you want to show any progress or information in the main screen, like a progress bar showing the progress of the operation you are doing in the background.

protected void onPostExecute(Z z){

}
This method is called after the operation in the background is done. As an input parameter you will receive the output parameter of the doInBackground method.

What about the X, Y and Z types?

As you can deduce from the above structure:

<pre><code>X – The type of the input variables value you want to set to the background process. This can be an array of objects.

 Y – The type of the objects you are going to enter in the onProgressUpdate method.

 Z – The type of the result from the operations you have done in the background process.
</code></pre>

How do we call this task from an outside class? Just with the following two lines:

<pre><code>MyTask myTask = new MyTask();

myTask.execute(x);
</code></pre>

Where x is the input parameter of the type X.

Once we have our task running, we can find out its status from “outside”. Using the “getStatus()” method.

myTask.getStatus();
and we can receive the following status:

RUNNING - Indicates that the task is running.

PENDING - Indicates that the task has not been executed yet.

FINISHED - Indicates that onPostExecute(Z) has finished.

Hints about using AsyncTask

Do not call the methods onPreExecute, doInBackground and onPostExecute manually. This is automatically done by the system.

You cannot call an AsyncTask inside another AsyncTask or Thread. The call of the method execute must be done in the UI Thread.

The method onPostExecute is executed in the UI Thread (here you can call another AsyncTask!).

The input parameters of the task can be an Object array, this way you can put whatever objects and types you want.

blocks|key|1004189|text|您可以在任务构造函数中传递参数，也可以在调用execute时传递参数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1004190|AsyncTask<Object,+Void,+MyTaskResult>|code-block|syntax|javascript|1004191|第一个参数(Object)在doInBackground中传递。第三个参数(MyTaskResult)由doInBackground返回。您可以将它们更改为所需的类型。这三个点表示零个或多个对象(或它们的数组)可以作为参数传递。|1004192|public+class+MyActivity+extends+AppCompatActivity+{

++++TextView+textView1;
++++TextView+textView2;

++++@Override
++++protected+void+onCreate(Bundle+savedInstanceState)+{
++++++++super.onCreate(savedInstanceState);
++++++++setContentView(R.layout.activity_main2);++++
++++++++textView1+=+(TextView)+findViewById(R.id.textView1);
++++++++textView2+=+(TextView)+findViewById(R.id.textView2);

++++++++String+input1+=+"test";
++++++++boolean+input2+=+true;
++++++++int+input3+=+100;
++++++++long+input4+=+100000000;

++++++++new+MyTask(input3,+input4).execute(input1,+input2);
++++}

++++private+class+MyTaskResult+{
++++++++String+text1;
++++++++String+text2;
++++}

++++private+class+MyTask+extends+AsyncTask<Object,+Void,+MyTaskResult>+{
++++++++private+String+val1;
++++++++private+boolean+val2;
++++++++private+int+val3;
++++++++private+long+val4;


++++++++public+MyTask(int+in3,+long+in4)+{
++++++++++++this.val3+=+in3;
++++++++++++this.val4+=+in4;

++++++++++++//+Do+something+...
++++++++}

++++++++protected+void+onPreExecute()+{
++++++++++++//+Do+something+...
++++++++}

++++++++@Override
++++++++protected+MyTaskResult+doInBackground(Object...+params)+{
++++++++++++MyTaskResult+res+=+new+MyTaskResult();
++++++++++++val1+=+(String)+params[0];
++++++++++++val2+=+(boolean)+params[1];

++++++++++++//Do+some+lengthy+operation++++
++++++++++++res.text1+=+RunProc1(val1);
++++++++++++res.text2+=+RunProc2(val2);

++++++++++++return+res;
++++++++}

++++++++@Override
++++++++protected+void+onPostExecute(MyTaskResult+res)+{
++++++++++++textView1.setText(res.text1);
++++++++++++textView2.setText(res.text2);

++++++++}
++++}

}|1004193|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|$]]

You can either pass the parameter in the task constructor or when you call execute:

<pre><code>AsyncTask&lt;Object, Void, MyTaskResult&gt;
</code></pre>

The first parameter (Object) is passed in doInBackground.
The third parameter (MyTaskResult) is returned by doInBackground. You can change them to the types you want. The three dots mean that zero or more objects (or an array of them) may be passed as the argument(s).

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

 TextView textView1;
 TextView textView2;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main2); 
 textView1 = (TextView) findViewById(R.id.textView1);
 textView2 = (TextView) findViewById(R.id.textView2);

 String input1 = "test";
 boolean input2 = true;
 int input3 = 100;
 long input4 = 100000000;

 new MyTask(input3, input4).execute(input1, input2);
 }

 private class MyTaskResult {
 String text1;
 String text2;
 }

 private class MyTask extends AsyncTask&lt;Object, Void, MyTaskResult&gt; {
 private String val1;
 private boolean val2;
 private int val3;
 private long val4;


 public MyTask(int in3, long in4) {
 this.val3 = in3;
 this.val4 = in4;

 // Do something ...
 }

 protected void onPreExecute() {
 // Do something ...
 }

 @Override
 protected MyTaskResult doInBackground(Object... params) {
 MyTaskResult res = new MyTaskResult();
 val1 = (String) params[0];
 val2 = (boolean) params[1];

 //Do some lengthy operation 
 res.text1 = RunProc1(val1);
 res.text2 = RunProc2(val2);

 return res;
 }

 @Override
 protected void onPostExecute(MyTaskResult res) {
 textView1.setText(res.text1);
 textView2.setText(res.text2);

 }
 }

}
</code></pre>

I use an <code>AsyncTask</code> for loading operations that I implemented as an inner class. 

In <code>onPreExecute()</code> I show a loading dialog which I then hide again in <code>onPostExecute()</code>. But for some of the loading operations I know in advance that they will finish very quickly so I don't want to display the loading dialog. 

I wanted to indicate this by a boolean parameter that I could pass to <code>onPreExecute()</code> but apparently for some reason <code>onPreExecute()</code> doesn't take any parameters.

The obvious workaround would probably be to create a member field in my AsyncTask or in the outer class which I would have to set before every loading operation but that does not seem very elegant. Is there a better way to do this?

Android: How can I pass parameters to AsyncTask's onPreExecute()?

Android

我使用AsyncTask加载作为内部类实现的操作。在onPreExecute()中，我显示了一个加载对话框，然后在onPostExecute()中再次将其隐藏。但是对于一些加载操作，我预先知道它们会很快完成，所以我不想显示加载对话框。我想通过一个可以传递给onPreExecute()的布尔型参数来表示这一点，但是显然由...

问Android:如何向异步任务的onPreExecute()传递参数？
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