Android 双缓冲 使用 示例

本文参考文献：《疯狂Android讲义（第2版）》

自定义视图：

package com.toby.personal.testlistview;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.MaskFilter;
import android.graphics.Paint;
import android.graphics.Path;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by toby on 2017/4/10.
 */

public class DrawView extends View {

    private final static int VIEW_WIDTH = 720;
    private final static int VIEW_HEIGHT = 1280;

    private float preX;
    private float preY;
    private Path path;
    private Paint paint = null;
    private Paint bmpPaint = null;
    private Bitmap cacheBitmap = null;
    private Canvas cacheCanvas = null;

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

        cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH, VIEW_HEIGHT, Bitmap.Config.ARGB_8888);
        cacheCanvas = new Canvas();
        path = new Path();
        cacheCanvas.setBitmap(cacheBitmap);

        paint = new Paint(Paint.DITHER_FLAG);
        paint.setColor(Color.RED);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(1);
        paint.setAntiAlias(true);
        paint.setDither(true);

        bmpPaint = new Paint();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        float x = event.getX();
        float y = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                path.moveTo(x, y);
                preX = x;
                preY = y;
                break;
            case MotionEvent.ACTION_MOVE:
                path.quadTo(preX, preY, x, y);
                preX = x;
                preY = y;
                break;
            case MotionEvent.ACTION_UP:
                cacheCanvas.drawPath(path, paint);
                path.reset();
                break;
        }
        invalidate();
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);
        canvas.drawPath(path, paint);
    }

    public void setColor(int color){
        paint.setColor(color);
    }

    public void setStrokeWidth(float width){
        paint.setStrokeWidth(width);
    }

    public void setMaskFilter(MaskFilter maskFilter){
        paint.setMaskFilter(maskFilter);
    }
}

自定义 menu 资源文件：

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:title="@string/color">
        <menu>
            <group android:checkableBehavior="single">
                <item
                    android:id="@+id/red"
                    android:title="@string/color_red" />
                <item
                    android:id="@+id/green"
                    android:title="@string/color_green" />
                <item
                    android:id="@+id/blue"
                    android:title="@string/color_blue" />
            </group>
        </menu>
    </item>

    <item android:title="@string/width">
        <menu>
            <group>
                <item
                    android:id="@+id/width_1"
                    android:title="@string/width_1" />
                <item
                    android:id="@+id/width_3"
                    android:title="@string/width_3" />
                <item
                    android:id="@+id/width_5"
                    android:title="@string/width_5" />
            </group>
        </menu>
    </item>

    <item
        android:id="@+id/blur"
        android:title="@string/blur" />

    <item
        android:id="@+id/emboss"
        android:title="@string/emboss" />
</menu>

主布局文件的内容：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorGray"
    android:orientation="vertical"
    android:id="@+id/container"
    >

    <com.toby.personal.testlistview.DrawView
        android:id="@+id/drawView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

主程序文件的内容：

package com.toby.personal.testlistview;

import android.graphics.BlurMaskFilter;
import android.graphics.Color;
import android.graphics.EmbossMaskFilter;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;

public class MainActivity extends AppCompatActivity {

    final private static String TAG = "Toby_Test";

    EmbossMaskFilter emboss;
    BlurMaskFilter blur;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        emboss = new EmbossMaskFilter(new float[]{1.5f, 1.5f, 1.5f}, 0.6f, 6, 4.2f);
        blur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = new MenuInflater(this);
        inflater.inflate(R.menu.test_menu01, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        DrawView drawView = (DrawView) findViewById(R.id.drawView);

        switch (item.getItemId()){
            case R.id.red:
                drawView.setColor(Color.RED);
                item.setChecked(true);
                break;
            case R.id.green:
                drawView.setColor(Color.GREEN);
                item.setChecked(true);
                break;
            case R.id.blue:
                drawView.setColor(Color.BLUE);
                item.setChecked(true);
                break;
            case R.id.width_1:
                drawView.setStrokeWidth(1);
                break;
            case R.id.width_3:
                drawView.setStrokeWidth(3);
                break;
            case R.id.width_5:
                drawView.setStrokeWidth(5);
                break;
            case R.id.blur:
                drawView.setMaskFilter(blur);
                break;
            case R.id.emboss:
                drawView.setMaskFilter(emboss);
                break;
        }

        return true;
    }
}

运行效果：

显示效果