问题描述
自从Android Studio在几天前更新以来，我一直遇到渲染问题。emuator将无法运行该应用程序，并会继续崩溃。我相信也许我已经为paintView使用的代码现在已被严重弃用了？问题栈是：
java.lang.NullPointerException
at com.example.drawnfire.paintView.onDraw_Original(paintView.java:112)
at com.example.drawnfire.paintView.onDraw(paintView.java)
at android.view.View.draw_Original(View.java:21443)
at android.view.View_Delegate.draw(View_Delegate.java:56)
at android.view.View.draw(View.java:21417)
at android.view.View.draw_Original(View.java:21317)
at android.view.View_Delegate.draw(View_Delegate.java:68)
at android.view.View.draw(View.java:21089)
at android.view.ViewGroup.drawChild(ViewGroup.java:4388)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4149)
at androidx.constraintlayout.widget.ConstraintLayout.dispatchDraw(ConstraintLayout.java:1963)
at android.view.View.draw_Original(View.java:21315)
at android.view.View_Delegate.draw(View_Delegate.java:68)
at android.view.View.draw(View.java:21089)
at android.view.ViewGroup.drawChild(ViewGroup.java:4388)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4149)
at android.view.View.draw_Original(View.java:21315)
at android.view.View_Delegate.draw(View_Delegate.java:68)
at android.view.View.draw(View.java:21089)
at android.view.ViewGroup.drawChild(ViewGroup.java:4388)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4149)
at android.view.View.draw_Original(View.java:21315)
at android.view.View_Delegate.draw(View_Delegate.java:68)
at android.view.View.draw(View.java:21089)
at android.view.ViewGroup.drawChild(ViewGroup.java:4388)
at android.view.ViewGroup.dispatchDraw(ViewGroup.java:4149)
at android.view.View.draw_Original(View.java:21446)
at android.view.View_Delegate.draw(View_Delegate.java:56)
at android.view.View.draw(View.java:21417)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.renderAndbuildresult(RenderSessionImpl.java:552)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.render(RenderSessionImpl.java:449)
at com.android.layoutlib.bridge.BridgeRenderSession.render(BridgeRenderSession.java:123)
at com.android.ide.common.rendering.api.RenderSession.render(RenderSession.java:143)
at com.android.ide.common.rendering.api.RenderSession.render(RenderSession.java:125)
at com.android.tools.idea.rendering.RenderTask.lambda$null$11(RenderTask.java:966)
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1604)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
，此代码所指的是：
import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.util.displayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.widget.Toast;
import java.util.ArrayList;
public class paintView extends View {
public static int Brush_SIZE = 10;
public static final int DEFAULT_COLOR = Color.RED;
public static final int DEFAULT_BG_COLOR = Color.WHITE;
private static final float TOUCH_TOLERANCE = 4;
private float mX,mY;
public LayoutParams params;
private Path mPath;
private Paint mPaint;
private int currentColor;
private int backgroundColor = DEFAULT_BG_COLOR;
private int strokeWidth;
private Bitmap mBitmap;
private Canvas mCanvas;
private Paint mBitmapPaint = new Paint(Paint.DITHER_FLAG);
private ArrayList<Draw> paths = new ArrayList<>();
private ArrayList<Draw> undo = new ArrayList<>();
public paintView(Context context) {
super(context);
init();
}
public paintView(Context context,AttributeSet attrs) {
super(context,attrs);
init();
}
public paintView(Context context,AttributeSet attrs,int defStyle) {
super(context,attrs,defStyle);
init();
}
private void init() {
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(DEFAULT_COLOR);
mPaint.setStyle(Paint.Style.stroke);
mPaint.setstrokeJoin(Paint.Join.ROUND);
mPaint.setstrokeCap(Paint.Cap.ROUND);
mPaint.setXfermode(null);
mPaint.setAlpha(0xff);
params = new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.WRAP_CONTENT);
}
public void clear() {
backgroundColor = DEFAULT_BG_COLOR;
paths.clear();
invalidate();
}
public void undo() {
if (paths.size() > 0) {
undo.add(paths.remove(paths.size() - 1));
invalidate(); // add
} else {
Toast.makeText(getContext(),"nothing to undo",Toast.LENGTH_LONG).show();
}
}
public void redo () {
if (undo.size() > 0) {
paths.add(undo.remove(undo.size() - 1));
invalidate(); // add
} else {
Toast.makeText(getContext(),Toast.LENGTH_LONG).show();
}
}
public void setstrokeWidth (int width) {
strokeWidth = width;
}
public void setColor (int color) {
currentColor = color;
}
public void initialise(displayMetrics displayMetrics) {
int height = displayMetrics.heightPixels;
int width = displayMetrics.widthPixels;
mBitmap = Bitmap.createBitmap(width,height,Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
currentColor = DEFAULT_COLOR;
strokeWidth = Brush_SIZE;
}
protected void onDraw(Canvas canvas) {
canvas.save();
mCanvas.drawColor(backgroundColor);
for (Draw draw : paths) {
mPaint.setColor(draw.color);
mPaint.setstrokeWidth(draw.strokeWidth);
mPaint.setMaskFilter(null);
mCanvas.drawPath(draw.path,mPaint);
}
canvas.drawBitmap(mBitmap,mBitmapPaint);
canvas.restore();
}
private void touchStart(float x,float y) {
mPath = new Path();
Draw draw = new Draw(currentColor,strokeWidth,mPath);
paths.add(draw);
mPath.reset();
mPath.moveto(x,y);
mX = x;
mY = y;
}
private void touchMove(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 touchUp() {
mPath.lineto(mX,mY);
}
@SuppressLint("ClickableViewAccessibility")
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
touchStart(x,y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touchUp();
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touchMove(x,y);
invalidate();
break;
}
return true;
}
}
我为此道歉，但是我对此失去了理智。
解决方法
Android Studio 4.0.0可以正常运行，但是4.1.0和4.2.0出现错误，并且不稳定。所以请使用Android Studio 4.0.0谢谢