问Android的图像按钮问题

EN

     java.lang.RuntimeException: Unable to start activity  
     ComponentInfo{com.example.admin.
     tetrisapp/com.example.admin.tetrisapp.MainActivity}: 
     android.view.InflateException: Binary XML file line #28: Error inflating 
     class ImageButton
     Caused by: android.content.res.Resources$NotFoundException: Resource is 
     not a Drawable (color or path): TypedValue{t=0x1/d=0x7f060056 a=-1 
     r=0x7f060056}

<android.support.constraint.ConstraintLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<LinearLayout
    android:id="@+id/linearLayout"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:visibility="visible"
    android:weightSum="1"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

    <RelativeLayout
        android:id="@+id/relativelayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_weight="0.3">

        <ImageButton
            android:id="@+id/rightButton"
            android:layout_width="50dp"
            android:layout_height="50dp"
            android:layout_above="@+id/downButton"
            android:layout_alignParentEnd="true"
            android:layout_marginEnd="40dp"
            android:src="@drawable/square"/>

    </RelativeLayout>
</LinearLayout>

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
 }
}