Android 生命周期 - View

AndroidRefine 2016-11

系列博文：

Android 生命周期 - Activity
Android 生命周期 - Service
Android 生命周期 - BroadcastReceiver
Android 生命周期 - Fragment
Android 生命周期 - View

View常见方法说明

View中的常见方法简单介绍如下：

• onFinishInflate(): 该方法当View及其子View从XML文件中加载完成后会被调用
• onMeasure(int, int)：该方法在计算当前View及其所有子View尺寸大小需求时会被调用。
• onLayout(boolean, int, int, int, int)：该方法在当前View需要为其子View分配尺寸和位置时会被调用。
• onSizeChanged(int, int, int, int)：该方法在当前View尺寸变化时被调用。
• onDraw(android.graphics.Canvas)：该方法在当前View需要呈现其内容时被调用。
• onFocusChanged(boolean, int, android.graphics.Rect)：该方法在当前View获得或失去焦点时被调用。
• onWindowFocusChanged(boolean)：该方法在包含当前View的window获得或失去焦点时被调用。
• onAttachedToWindow()：该方法在当前View被附到一个window上时被调用。
• onDetachedFromWindow()：该方法在当前View从一个window上分离时被调用。
• onVisibilityChanged(View, int)：该方法在当前View或其祖先的可见性改变时被调用。
• onWindowVisibilityChanged(int)：该方法在包含当前View的window可见性改变时被调用。

Java代码

BCView.java

public class BCView extends View {
    @Override
    protected void onVisibilityChanged(View changedView, int visibility) {
        super.onVisibilityChanged(changedView, visibility);
        Log.i(MainActivity.TAG, "BCView onVisibilityChanged(View changedView, int visibility) changedView = " + visibility);
    }
    public BCView(Context context, AttributeSet attrs) {
        super(context, attrs);
        Log.i(MainActivity.TAG, "BCView BCView(Context context, AttributeSet attrs)");
    }
    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        Log.i(MainActivity.TAG, "BCView onAttachedToWindow()");
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        Log.i(MainActivity.TAG, "BCView onMeasure(int widthMeasureSpec, int heightMeasureSpec) widthMeasureSpec = " + widthMeasureSpec + " heightMeasureSpec =  " + heightMeasureSpec);
    }
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        Log.i(MainActivity.TAG, "BCView onSizeChanged(int w, int h, int oldw, int oldh)");
    }
    @Override
    protected void onFocusChanged(boolean gainFocus, int direction, Rect previouslyFocusedRect) {
        super.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
        Log.i(MainActivity.TAG, "BCView onFocusChanged(boolean gainFocus, int direction, Rect previouslyFocusedRect)");
    }
    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        Log.i(MainActivity.TAG, "BCView onFinishInflate()");
    }
    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        Log.i(MainActivity.TAG, "BCView onLayout(boolean changed, int left, int top, int right, int bottom) changed = " + changed + " left = " + left + " top = " + top + " right = " + right + " bottom = " + bottom);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Log.i(MainActivity.TAG, "BCView onDraw(Canvas canvas)");
    }
    @Override
    public void onWindowFocusChanged(boolean hasWindowFocus) {
        super.onWindowFocusChanged(hasWindowFocus);
        Log.i(MainActivity.TAG, "BCView onWindowFocusChanged(boolean hasWindowFocus) hasWindowFocus = " + hasWindowFocus);
    }
    @Override
    protected void onWindowVisibilityChanged(int visibility) {
        super.onWindowVisibilityChanged(visibility);
        Log.i(MainActivity.TAG, "BCView onWindowVisibilityChanged(int visibility) visibility = " + visibility);
    }
    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        Log.i(MainActivity.TAG, "BCView onDetachedFromWindow()");
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {
    public static final String TAG = "mutex";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.i(TAG, "MainActivity onCreate()");
    }
}

资源文件

activity.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="fresco.mutex.com.lifecycle.MainActivity">
    <fresco.mutex.com.lifecycle.BCView
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_centerInParent="true"
        android:background="@android:color/holo_blue_light" />
</RelativeLayout>

启动以后，查看Log日志

Log日志

• 从启动到View显示完整的生命周期如上所示，可以小结出大的轮廓如下：

  Constructors()构造器 ---->> onFinishInflate() ---->> onAttachedToWindow --->> onMeasure ---->> onLayout() --->> onDraw()

• 接着Back回退
  

onWindowFocusChanged --->> onWindowVisibilityChanged --->> onDetachedFromWindow

接下来将上面的BCView属性设置invisible如下：

<fresco.mutex.com.lifecycle.BCView
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_below="@id/activity_main_send"
        android:layout_centerInParent="true"
        android:visibility="invisible"
        android:background="@android:color/holo_blue_light" />

• 再看一下启动到显示View后的Log日志
  
  可以看到生命周期有所不同，前面多了个onVisibilityChanged()方法，后面缺少了onDraw()方法。
• 接着Back回退
  

最后，我们将BCView的属性设置为Gone如下：

<fresco.mutex.com.lifecycle.BCView
        android:layout_width="80dp"
        android:layout_height="80dp"
        android:layout_below="@id/activity_main_send"
        android:layout_centerInParent="true"
        android:visibility="gone"
        android:background="@android:color/holo_blue_light" />

• 在看一下启动到显示View后的Log日志
  
  可以看到生命周期方法少了很多，不仅少了onDraw()方法，同时onMeasure()以及onLayout()方法也没有了。
• 接着Back回退
  

小结

• View默认为可见的，否则先调用onVisibilityChanged()，但是此时该View的长宽以及位置等信息都不知道。
• 如果View是invisible，则不会回调onDraw()方法
• 如果View是gone，则不会回调onMeasure()，onLayout()，onDraw()方法
• 不管View是什么状态，总是会回调onAttachedToWindow()以及onDetachedFromWindow()方法
• View的销毁流程和可见性没有关系
• [onVisibilityChanged()可选] --> 构造器View() --> onFinishInflate() --> onAttachedToWindow() --> onMeasure() --> onSizeChanged() --> onLayout() --> onDraw() --> onDetackedFromWindow()