【Android】【UI】如何判断控件完全加载完毕

原理

控件的加载流程如下： 解析布局 - 绑定窗口 - 测量自身大小 - 计算子控件布局 - 绘制

所以，在onMeasure结束，或onLayout开始的时候，View自身就已经完全解析完成了 此时就可以正确获取控件大小了，很多控件，只有在知道自身大小之后，UI方法才能正确执行

测试代码

	public class TTView extends View {
	
	    public TTView(Context context) {
	        super(context);
	    }
	
	    public TTView(Context context, AttributeSet attributeSet) {
	        super(context, attributeSet);
	    }
	
	    @Override
	    protected void onFinishInflate() {
	        Console.info("TTView", "onFinishInflate", getMeasuredWidth());
	        super.onFinishInflate();
	    }
	
	    @Override
	    protected void onAttachedToWindow() {
	        Console.info("TTView", "onAttachedToWindow", getMeasuredWidth());
	        super.onAttachedToWindow();
	    }
	
	    @Override
	    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	        Console.info("TTView", "onMeasure", getMeasuredWidth());
	        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	    }
	
	    @Override
	    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
	        Console.info("TTView", "onLayout", getMeasuredWidth());
	        super.onLayout(changed, left, top, right, bottom);
	    }
	
	    @Override
	    protected void onDraw(Canvas canvas) {
	        Console.info("TTView", "onDraw", getMeasuredWidth());
	        super.onDraw(canvas);
	    }
	
	    @Override
	    protected void onVisibilityChanged(View changedView, int visibility) {
	        Console.info("TTView", "onVisibilityChanged", getMeasuredWidth());
	        super.onVisibilityChanged(changedView, visibility);
	    }
	
	    @Override
	    protected void onFocusChanged(boolean gainFocus, int direction, Rect previouslyFocusedRect) {
	        Console.info("TTView", "onFocusChanged", getMeasuredWidth());
	        super.onFocusChanged(gainFocus, direction, previouslyFocusedRect);
	    }
	}

	2020-10-27 18:38:56.836 27117-27117/com.aodun.app.bundle W/com.easing.commons: [TTView, onFinishInflate, 0]
	2020-10-27 18:38:56.875 27117-27117/com.aodun.app.bundle W/com.easing.commons: [TTView, onAttachedToWindow, 0]
	2020-10-27 18:38:56.875 27117-27117/com.aodun.app.bundle W/com.easing.commons: [TTView, onVisibilityChanged, 0]
	2020-10-27 18:38:56.880 27117-27117/com.aodun.app.bundle W/com.easing.commons: [TTView, onMeasure, 0]
	2020-10-27 18:38:56.889 27117-27117/com.aodun.app.bundle W/com.easing.commons: [TTView, onMeasure, 563]
	2020-10-27 18:38:56.891 27117-27117/com.aodun.app.bundle W/com.easing.commons: [TTView, onLayout, 563]
	2020-10-27 18:38:56.901 27117-27117/com.aodun.app.bundle W/com.easing.commons: [TTView, onDraw, 563]
	2020-10-27 18:38:57.004 27117-27117/com.aodun.app.bundle W/com.easing.commons: [TTView, onLayout, 563]

可以看到，onLayout执行时，控件大小就确定了，我们可以以这个方法作为控件加载完毕的标志

应用

如果我们有一些操作，需要等控件加载完毕才执行 可以在onLayout中添加一个回调，通过回调就可以告知外界，自身加载完毕了

	@Override
	protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
	    if(layoutCompleteListener != null)
	        layoutCompleteListener.onLayoutComplete();
	    super.onLayout(changed, left, top, right, bottom);
	}

延伸

采用同样的测试方法，我们可以找到Activity布局完全加载的标志 那就是handler.post(runnable)方法，经常测试我们可以得知，handler.post只有在布局完全加载完成时才会执行 如果我们想等布局加载完成再执行代码，将代码写在runnable中，通过handler发送即可