Question

我创建了自定义thread，并使用postInvalidate方法调用并移动图片，但我的Null Pointer Exception有Thread class AnimThread for PostInvalidate。

package com.example.ahmad.ballmoving;
    import android.view.View;
    /**
     * Created by Ahmad on 7/30/2015.
     */
    public class AnimThread extends Thread {
        private View threadView;
        public AnimThread(View view )
        {
            if(view!=null) {
                threadView = view;
            }
        }

        @Override
        public void run()
        {
            while(true) {
                try {
                    Thread.sleep(1000);
                    threadView.postInvalidate();

                    } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

这是我的自定义视图类。

    package com.example.ahmad.ballmoving;
    import android.content.Context;
    import android.graphics.Bitmap;
    import android.graphics.BitmapFactory;
    import android.graphics.Canvas;
    import android.graphics.Color;
    import android.graphics.Paint;
    import android.graphics.Rect;
    import android.util.AttributeSet;
    import android.view.View;

    /**
     * Created by Ahmad on 7/29/2015.
     */
    public class MyContextView extends View
    {
        int xVelocity=1;
        int yVelocity=1;
        private Runnable runn;
        Bitmap imag1;
        int x=0,y=0;

        public MyContextView(Context context, AttributeSet att)
        {
            super(context);
  imag1=BitmapFactory.decodeResource(getResources(),R.drawable.images);
        }

        @Override
        protected void onDraw(Canvas canvas) {

            super.onDraw(canvas);

            x=x+xVelocity;
            y=y+yVelocity;
           //canvas.save();
            //invalidate();
            canvas.drawBitmap(imag1, x, y, null);

        }
    }

这是我的主要课程

package com.example.ahmad.ballmoving;
    import android.support.v7.app.ActionBarActivity;
    import android.os.Bundle;
    import android.view.Menu;
    import android.view.MenuItem;
    public class MainActivity extends ActionBarActivity {
        private Thread thread1;
        private Thread thread2;
        public MyContextView mcv;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            MyContextView c = (MyContextView)findViewById(R.id.ko);
            Thread a = new AnimThread(c);
            a.start();
        } 
    }

这是我的主类XML：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <com.example.ahmad.ballmoving.MyContextView
        android:layout_height="fill_parent"
        android:layout_width="fill_parent"
        android:id="@+id/ko"/>


</RelativeLayout>

Answer 1

您可以尝试 CountDownTimer 吗？

new CountDownTimer(1000,100) {

        @Override
        public void onTick(long millisUntilFinished) {

        }

        @Override
        public void onFinish() {

            threadView.postInvalidate();

        }
    }.start();

希望这会对你有所帮助。

在线程类中调用postInvalidate方法时出现空指针异常

1 个答案: