OnAttachStateChangeListener

概述

/**
 * Interface definition for a callback to be invoked when this view is attached
 * or detached from its window.
 */
public interface OnAttachStateChangeListener {
    /**
     * Called when the view is attached to a window.
     * @param v The view that was attached
     */
    public void onViewAttachedToWindow(View v);
    /**
     * Called when the view is detached from a window.
     * @param v The view that was detached
     */
    public void onViewDetachedFromWindow(View v);
}

当你的view attach 或者 detach到window的时候都会回调这个接口，我们可以测试一下在什么时候view会attach 和detach 到window上

1.

package com.example.jinxiong.onattachstatechange.view;

import android.content.Context;
import android.graphics.Canvas;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;

/**
 * Created by jinxiong on 2017/3/20.
 */

public class MyView extends android.support.v7.widget.AppCompatTextView implements View.OnAttachStateChangeListener {

private static final String TAG = "MainActivity";

public MyView(Context context) {
    super(context);
    init();
}

public MyView(Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
    init();

}

public MyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    init();
}

void init() {
    this.addOnAttachStateChangeListener(this);
}


@Override
public void onViewAttachedToWindow(View v) {
    Log.d(TAG, "onViewAttachedToWindow: ");
}

@Override
public void onViewDetachedFromWindow(View v) {
    Log.d(TAG, "onViewDetachedFromWindow: ");
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    Log.d(TAG, "onMeasure: ");
}

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    super.onLayout(changed, left, top, right, bottom);
    Log.d(TAG, "onLayout: ");
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Log.d(TAG, "onDraw: ");

}
}

重写TextView，为它增加onAttachStateChageListener,

package com.example.jinxiong.onattachstatechange;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;

public class MainActivity extends AppCompatActivity {

private static final String TAG = "MainActivity";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.d(TAG, "onCreate: 之后");


    this.findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            setContentView(R.layout.test);
        }
    });
}

@Override
protected void onDestroy() {
    super.onDestroy();
    Log.d(TAG, "onDestroy: ");
}
}

在activity的onCreate 和 onDestroy方法中log，运行程序可以看到log如下：

03-19 21:37:07.851 15910-15910 D/MainActivity: onCreate: 之后
03-19 21:37:07.879 15910-15910 D/MainActivity: onViewAttachedToWindow: 
03-19 21:37:07.893 15910-15910 D/MainActivity: onMeasure: 
03-19 21:37:08.040 15910-15910 D/MainActivity: onMeasure: 
03-19 21:37:08.040 15910-15910 D/MainActivity: onLayout: 
03-19 21:37:08.109 15910-15910 D/MainActivity: onMeasure: 
03-19 21:37:08.109 15910-15910 D/MainActivity: onLayout: 
03-19 21:37:08.109 15910-15910 D/MainActivity: onDraw: 

按下返回键

03-19 21:42:12.001 15910-15910 D/MainActivity: onDestroy: 
03-19 21:42:12.002 15910-15910 D/MainActivity: onViewDetachedFromWindow:

结论1：在activity中，当执行完setContentView方法之后才会将view attach 到window上的，当执行完onDestroy后才会detach
在上面增加了一个button ,也设置了一个点击事件，点击之后会再次调用setContentView方法，将另外的布局文件替换到原先的布局文件，log如下：

03-19 21:47:16.498 15910-15910 D/MainActivity: onViewDetachedFromWindow: 

增加结论1：当执行完setContentView方法之后才会将view attach 到window上的，当执行完onDestroy后或者setContentView被再一次调用，view才会detach