当应用程序在后台时，Finger Paint 自定义视图绘图消失

Posted 2023-02-16

【中文标题】当应用程序在后台时，Finger Paint 自定义视图绘图消失

【英文标题】：FingerPaint custom view drawing dissapears when app in background

【发布时间】：2014-08-12 10:17:03

【问题描述】：

我正在为自己的绘图应用程序使用 android FingerPaint 示例。 我一切正常，但如果用户点击设备主页按钮，然后再次打开我的应用程序，他所做的所有绘图都会消失。

似乎正在重新创建视图，而不是之前的绘图。

我已经尝试过 onSaveInstanceState 和 onRestoreInstanceState 但从来没有调用，我不知道如何保存画图。

有什么办法解决这个问题吗？

Android FingerPaint 示例也有同样的问题。这是代码：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.graphics;

import android.content.Context;
import android.graphics.*;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;

public class FingerPaint extends GraphicsActivity
        implements ColorPickerDialog.OnColorChangedListener 

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(new MyView(this));

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(0xFFFF0000);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(12);

        mEmboss = new EmbossMaskFilter(new float[]  1, 1, 1 ,
                                       0.4f, 6, 3.5f);

        mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
    

    private Paint       mPaint;
    private MaskFilter  mEmboss;
    private MaskFilter  mBlur;

    public void colorChanged(int color) 
        mPaint.setColor(color);
    

    public class MyView extends View 

        private static final float MINP = 0.25f;
        private static final float MAXP = 0.75f;

        private Bitmap  mBitmap;
        private Canvas  mCanvas;
        private Path    mPath;
        private Paint   mBitmapPaint;

        public MyView(Context c) 
            super(c);

            mPath = new Path();
            mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        

        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) 
            super.onSizeChanged(w, h, oldw, oldh);
            mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);
        

        @Override
        protected void onDraw(Canvas canvas) 
            canvas.drawColor(0xFFAAAAAA);

            canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

            canvas.drawPath(mPath, mPaint);
        

        private float mX, mY;
        private static final float TOUCH_TOLERANCE = 4;

        private void touch_start(float x, float y) 
            mPath.reset();
            mPath.moveTo(x, y);
            mX = x;
            mY = y;
        
        private void touch_move(float x, float y) 
            float dx = Math.abs(x - mX);
            float dy = Math.abs(y - mY);
            if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) 
                mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
                mX = x;
                mY = y;
            
        
        private void touch_up() 
            mPath.lineTo(mX, mY);
            // commit the path to our offscreen
            mCanvas.drawPath(mPath, mPaint);
            // kill this so we don't double draw
            mPath.reset();
        

        @Override
        public boolean onTouchEvent(MotionEvent event) 
            float x = event.getX();
            float y = event.getY();

            switch (event.getAction()) 
                case MotionEvent.ACTION_DOWN:
                    touch_start(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_MOVE:
                    touch_move(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_UP:
                    touch_up();
                    invalidate();
                    break;
            
            return true;
        
    

    private static final int COLOR_MENU_ID = Menu.FIRST;
    private static final int EMBOSS_MENU_ID = Menu.FIRST + 1;
    private static final int BLUR_MENU_ID = Menu.FIRST + 2;
    private static final int ERASE_MENU_ID = Menu.FIRST + 3;
    private static final int SRCATOP_MENU_ID = Menu.FIRST + 4;

    @Override
    public boolean onCreateOptionsMenu(Menu menu) 
        super.onCreateOptionsMenu(menu);

        menu.add(0, COLOR_MENU_ID, 0, "Color").setShortcut('3', 'c');
        menu.add(0, EMBOSS_MENU_ID, 0, "Emboss").setShortcut('4', 's');
        menu.add(0, BLUR_MENU_ID, 0, "Blur").setShortcut('5', 'z');
        menu.add(0, ERASE_MENU_ID, 0, "Erase").setShortcut('5', 'z');
        menu.add(0, SRCATOP_MENU_ID, 0, "SrcATop").setShortcut('5', 'z');

        /****   Is this the mechanism to extend with filter effects?
        Intent intent = new Intent(null, getIntent().getData());
        intent.addCategory(Intent.CATEGORY_ALTERNATIVE);
        menu.addIntentOptions(
                              Menu.ALTERNATIVE, 0,
                              new ComponentName(this, NotesList.class),
                              null, intent, 0, null);
        *****/
        return true;
    

    @Override
    public boolean onPrepareOptionsMenu(Menu menu) 
        super.onPrepareOptionsMenu(menu);
        return true;
    

    @Override
    public boolean onOptionsItemSelected(MenuItem item) 
        mPaint.setXfermode(null);
        mPaint.setAlpha(0xFF);

        switch (item.getItemId()) 
            case COLOR_MENU_ID:
                new ColorPickerDialog(this, this, mPaint.getColor()).show();
                return true;
            case EMBOSS_MENU_ID:
                if (mPaint.getMaskFilter() != mEmboss) 
                    mPaint.setMaskFilter(mEmboss);
                 else 
                    mPaint.setMaskFilter(null);
                
                return true;
            case BLUR_MENU_ID:
                if (mPaint.getMaskFilter() != mBlur) 
                    mPaint.setMaskFilter(mBlur);
                 else 
                    mPaint.setMaskFilter(null);
                
                return true;
            case ERASE_MENU_ID:
                mPaint.setXfermode(new PorterDuffXfermode(
                                                        PorterDuff.Mode.CLEAR));
                return true;
            case SRCATOP_MENU_ID:
                mPaint.setXfermode(new PorterDuffXfermode(
                                                    PorterDuff.Mode.SRC_ATOP));
                mPaint.setAlpha(0x80);
                return true;
        
        return super.onOptionsItemSelected(item);
    

【问题讨论】：

请添加您的代码

我已经用这些帮助类测试了这段代码：gitorious.org/freebroid/development/source/… 并且工作正常。在我的三星 Galaxy Nexus 上测试

在我的 Nexus 5 中它无法正常工作，如果我切换前台应用程序，它会擦除​​我的所有绘图。

对不起，我帮不了你。我无法重现该问题:(

如果您旋转设备，所有绘图都会丢失。你知道怎么保存吗？

【参考方案1】：

Check this answer - Android: onSaveInstanceState not being called from activity

您可能需要将项目存储在您的共享首选项或文件或数据库中，以确保正确保存和恢复这些值。

希望有帮助！