在我的手机上运行这个Android appp时，当我点击启动应用程序并且logcat显示以下错误时，它会突然崩溃。
> 07-24 14:54:03.291
> 15207-15207/com.example.parthibank.needleandroidproj E/AndroidRuntime:
> FATAL EXCEPTION: main
> Process: com.example.parthibank.needleandroidproj, PID: 15207
> java.lang.RuntimeException: Unable to instantiate activity
> ComponentInfo{com.example.parthibank.needleandroidproj/com.example.parthibank.needleandroidproj.MainActivity}:
> java.lang.InstantiationException:
> java.lang.Class<com.example.parthibank.needleandroidproj.MainActivity>
> has no zero argument constructor
> at
> android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3133)
> at
> android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3416)
> at android.app.ActivityThread.access$1100(ActivityThread.java:229)
> at
> android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
> at android.os.Handler.dispatchMessage(Handler.java:102)
> at android.os.Looper.loop(Looper.java:148)
> at android.app.ActivityThread.main(ActivityThread.java:7407)
> at java.lang.reflect.Method.invoke(Native Method)
> at
> com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
> at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
> Caused by: java.lang.InstantiationException:
> java.lang.Class<com.example.parthibank.needleandroidproj.MainActivity>
> has no zero argument constructor
> at java.lang.Class.newInstance(Native Method)
> at android.app.Instrumentation.newActivity(Instrumentation.java:1096)
> at
> android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3123)
> at
> android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3416)
> at android.app.ActivityThread.access$1100(ActivityThread.java:229)
> at
> android.app.ActivityThread$H.handleMessage(ActivityThread.java:1821)
> at android.os.Handler.dispatchMessage(Handler.java:102)
> at android.os.Looper.loop(Looper.java:148)
> at android.app.ActivityThread.main(ActivityThread.java:7407)
> at java.lang.reflect.Method.invoke(Native Method)
> at
> com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
> at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
我无法理解它要求的是哪个构造函数。请指导
package com.example.parthibank.needleandroidproj;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.RadialGradient;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.view.View;
public class MainActivity extends View {
private Paint linePaint;
private Path linePath;
private Paint needleScrewPaint;
private Matrix matrix;
private int framePerSeconds = 100;
private long animationDuration = 10000;
private long startTime;
public MainActivity(Context context) {
super(context);
matrix = new Matrix();
this.startTime = System.currentTimeMillis();
this.postInvalidate();
init();
}
public MainActivity(Context context, AttributeSet attrs) {
super(context, attrs);
matrix = new Matrix();
this.startTime = System.currentTimeMillis();
this.postInvalidate();
init();
}
public MainActivity(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
matrix = new Matrix();
this.startTime = System.currentTimeMillis();
this.postInvalidate();
init();
}
private void init(){
linePaint = new Paint();
linePaint.setColor(Color.RED); // Set the color
linePaint.setStyle(Paint.Style.FILL_AND_STROKE); // set the border and fills the inside of needle
linePaint.setAntiAlias(true);
linePaint.setStrokeWidth(5.0f); // width of the border
linePaint.setShadowLayer(8.0f, 0.1f, 0.1f, Color.GRAY); // Shadow of the needle
linePath = new Path();
linePath.moveTo(50.0f, 50.0f);
linePath.lineTo(130.0f, 40.0f);
linePath.lineTo(600.0f, 50.0f);
linePath.lineTo(130.0f, 60.0f);
linePath.lineTo(50.0f, 50.0f);
linePath.addCircle(130.0f, 50.0f, 20.0f, Path.Direction.CW);
linePath.close();
needleScrewPaint = new Paint();
needleScrewPaint.setColor(Color.BLACK);
needleScrewPaint.setAntiAlias(true);
needleScrewPaint.setShader(new RadialGradient(130.0f, 50.0f, 10.0f,
Color.DKGRAY, Color.BLACK, Shader.TileMode.CLAMP));
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
long elapsedTime = System.currentTimeMillis() - startTime;
matrix.postRotate(1.0f, 130.0f, 50.0f); // rotate 10 degree every second
canvas.concat(matrix);
canvas.drawPath(linePath, linePaint);
canvas.drawCircle(130.0f, 50.0f, 16.0f, needleScrewPaint);
if(elapsedTime < animationDuration){
this.postInvalidateDelayed(10000 / framePerSeconds);
}
//this.postInvalidateOnAnimation();
invalidate();
}
}
答案 0 :(得分：0)
您需要在constructor中定义 no-args class，如下所示：
public MainActivity() {
super();
}