ANDROID：自定义视图实现

Question

我有一个自定义视图。 android什么时候会调用draw()呢？在调用onMeasure和onLayout之后？

'package global.domination.pack;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.util.Log;
import android.view.View;

public class TileView extends View {

    // rules about what can be and is on this tile
    boolean bLand;
    boolean bSea;
    boolean bAir;
    boolean bOccupied;
    Character _character;

    // this tile's coordinates
    int nX;
    int nY;

    // bitmaps used for drawing this tile
    Bitmap _originalBitmap;
    Bitmap _finalBitmap;

    // this constructor initializes all variables (creates the tile)
    public TileView(Context context, boolean isLand, boolean isSea, boolean isAir, boolean isOccupied, int x_Coordinate, int y_Coordinate, Bitmap bitmap) {
        super(context);

        //Initialize variables and set tile graphic.
        bLand           = isLand;
        bSea            = isSea;
        bAir            = isAir;
        bOccupied       = isOccupied;
        nX              = x_Coordinate;
        nY              = y_Coordinate;
        _originalBitmap = bitmap;
        _character      = null;
        _finalBitmap    = bitmap;
    }


    /* This method is called by parent view when it 
     * wants to know this view's drawing preferences
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // set this tiles dimensions
        this.setMeasuredDimension(50, 50);
    }

    /* This method is called by parent view when it wants 
     * this view to draw itself.
     */
    @Override
    protected void onDraw(Canvas canvas) {      
        // attempt to draw the _finalBitmap (tile graphic with character graphic)
        try{
            canvas.drawBitmap(_finalBitmap, 0, 0, null);
        }
        catch(RuntimeException rtException){
            Log.e("EXCEPTION", "ERROR DRAWING FINAL BITMAP" + rtException.getMessage() , rtException);
        }               
    }
}
'

Answer 1

您是否覆盖了 ViewGroup 的 onMeasure() ？如果是这样，您需要记住在子视图上调用 measure() 。

Answer 2

每当视图必须测量其自身视图和子视图的尺寸时，总是会调用 onMeasure() 。
如果您要实现视图组，那么每当视图组必须在 onLayout() 之后向其所有子视图分派绘制事件时，就会调用其子视图的 onDraw() 方法。

这是一个图像链接，可以帮助您了解视图生命周期流程：

有关简要说明，您可以阅读官方文档。