Android開發 View的生命周期結合代碼詳解

咱們以TextView控制元件為例：

/**
 * Created by SunshineBoy on 2020/9/23.
 */
public class TestTextView extends android.support.v7.widget.AppCompatTextView {
    public TestTextView(Context context) {
        super(context);
        Log.e("TestTextView","TestTextView(Context context)");
    }

    public TestTextView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        Log.e("TestTextView","TestTextView(Context context, @Nullable AttributeSet attrs)");
    }

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

    @Override
    protected void onVisibilityChanged(View changedView, int visibility) {
        super.onVisibilityChanged(changedView, visibility);
        Log.e("TestTextView","onVisibilityChanged");
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        Log.e("TestTextView","onFinishInflate");
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        Log.e("TestTextView","onAttachedToWindow");
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        Log.e("TestTextView","onMeasure");
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        Log.e("TestTextView","onSizeChanged");
    }

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

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Log.e("TestTextView","onDraw");
    }

    @Override
    protected void onWindowVisibilityChanged(int visibility) {
        super.onWindowVisibilityChanged(visibility);
        Log.e("TestTextView","onWindowVisibilityChanged="+visibility);
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        Log.e("TestTextView","onDetachedFromWindow");
    }
}

先看看默認狀態下生命周期：

2020-09-23 17:34:40.882 15132-15132/com.freddy.chat E/TestTextView: TestTextView(Context context, @Nullable AttributeSet attrs)
2020-09-23 17:34:40.882 15132-15132/com.freddy.chat E/TestTextView: onFinishInflate
2020-09-23 17:34:40.927 15132-15132/com.freddy.chat E/TestTextView: onAttachedToWindow
2020-09-23 17:34:40.927 15132-15132/com.freddy.chat E/TestTextView: onWindowVisibilityChanged=0
2020-09-23 17:34:40.927 15132-15132/com.freddy.chat E/TestTextView: onVisibilityChanged
2020-09-23 17:34:40.928 15132-15132/com.freddy.chat E/TestTextView: onMeasure
2020-09-23 17:34:41.056 15132-15132/com.freddy.chat E/TestTextView: onMeasure
2020-09-23 17:34:41.056 15132-15132/com.freddy.chat E/TestTextView: onSizeChanged
2020-09-23 17:34:41.056 15132-15132/com.freddy.chat E/TestTextView: onLayout
2020-09-23 17:34:41.065 15132-15132/com.freddy.chat E/TestTextView: onDraw

接下來看看setVisibility(View.INVISIBLE)狀態：

2020-09-23 17:37:14.191 15132-15132/com.freddy.chat E/TestTextView: onVisibilityChanged

再看看setVisibility(View.VISIBLE)狀態：

2020-09-23 17:38:07.338 15132-15132/com.freddy.chat E/TestTextView: onVisibilityChanged
2020-09-23 17:38:07.535 15132-15132/com.freddy.chat E/TestTextView: onDraw

再看看離開Activity掛起狀態：

2020-09-23 17:39:33.128 15132-15132/com.freddy.chat E/TestTextView: onWindowVisibilityChanged=8
2020-09-23 17:39:33.267 15132-15132/com.freddy.chat E/TestTextView: onVisibilityChanged

然后Activity掛起恢復：

2020-09-23 17:40:32.178 15132-15132/com.freddy.chat E/TestTextView: onWindowVisibilityChanged=4
2020-09-23 17:40:32.361 15132-15132/com.freddy.chat E/TestTextView: onVisibilityChanged
2020-09-23 17:40:32.414 15132-15132/com.freddy.chat E/TestTextView: onWindowVisibilityChanged=0
2020-09-23 17:40:32.551 15132-15132/com.freddy.chat E/TestTextView: onDraw

最后再看看Activity銷毀狀態：

2020-09-23 17:41:31.610 15132-15132/com.freddy.chat E/TestTextView: onWindowVisibilityChanged=8
2020-09-23 17:41:31.837 15132-15132/com.freddy.chat E/TestTextView: onDetachedFromWindow

由上可知View的生命周期是：

1. 首先創建帶兩個引數的建構式；
2. 然后從xml檔案中inflate完成后調onFinishInflate方法；
3. 然后在Activity執行onResume之后依附Activity視窗調onAttachedToWindow方法；
4. 然后調視窗狀態發生改變調onWindowVisibilityChanged方法；
5. 然后調view的狀態發生改變調onVisibilityChanged方法；
6. 然后開始測量view尺寸調onMeasure方法；
7. 然后測量結果與上次測量結果不一致時調onSizeChanged方法；
8. 然后為子view分配位置調onLayout方法；
9. 然后view渲染繪制內容細節調onDraw方法；
10. 最后Activity銷毀時調onDetachedFromWindow方法，