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我正在尝试用我的自定义视图类做 addView 。但它根本不起作用。请查看我的代码和错误日志。我希望你能帮助我。

我做了一个内部服装视图。现在我想用 addView() 将它添加到我的布局 xml 中,所以它给出了一个空指针异常

代码:

package com.example.les14;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.support.v4.view.ViewPager.LayoutParams;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.LinearLayout;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;


public class MainActivity extends Activity implements OnTouchListener{
    MyView myView;
    int numberOfFingers = 0;
    float oldX[] = new float[2], oldY[] = new float[2];
    Rect rectangle = new Rect(0, 0, 100, 100);
    DisplayMetrics metrics = new DisplayMetrics();
     String radioButtonSelected = "";
     RadioGroup radioGroup;
     int checkedRadioButton = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyView myView = new MyView(this);
        LinearLayout layout = (LinearLayout) findViewById(R.id.mainlayout);
        layout.addView(myView);
        myView.setOnTouchListener(this);
    //  radioGroup = (RadioGroup) findViewById(R.id.radioGroup1);

        getWindowManager().getDefaultDisplay().getMetrics(metrics);
       //radioGroup.setOnCheckedChangeListener(this);

        setContentView(R.layout.activity_main);


    }
//  @Override
//  public void onCheckedChanged(RadioGroup radioGroup, int arg1) {
        // TODO Auto-generated method stub

    //}
   void radio(){


        int checkedRadioButton = radioGroup.getCheckedRadioButtonId();

        switch (checkedRadioButton) {
      case R.id.radio0 : radioButtonSelected = "AO1";
                                      break;
      case R.id.radio1 : radioButtonSelected = "AO2";
                                  break;

    }

    }
    public boolean onTouch(View view, MotionEvent event){
        switch(event.getActionMasked()) {
        case MotionEvent.ACTION_DOWN:
            numberOfFingers = 1;
            oldX[0] = event.getX(0);
            oldY[0] = event.getY(0);
            break;
        case MotionEvent.ACTION_POINTER_DOWN:
            numberOfFingers = 2;
            oldX[1] = event.getX(1);
            oldY[1] = event.getY(1);
            break;
        case MotionEvent.ACTION_MOVE:
            handleMove(event);
            break;
        case MotionEvent.ACTION_POINTER_UP:
        case MotionEvent.ACTION_UP:
            numberOfFingers--;
            break;
        }

        view.invalidate();
        return true;
    }

    public class MyView extends View {
        Paint redPaint = new Paint();

        public MyView(Context context) {
            super(context);


           redPaint.setColor(Color.RED);
        }


        public void onDraw(Canvas canvas){

            canvas.drawRect(rectangle, redPaint);
        }





    }

    float newX[] = new float[2], newY[] = new float[2];
    int xChange[] = new int[2], yChange[] = new int[2];
    int diffX, diffY;
    int newLeft = rectangle.left, newTop = rectangle.top,
            newRight = rectangle.right,
            newBottom = rectangle.bottom;

    void handleMove(MotionEvent event) {
        newX[0] = Math.round(event.getX(0));
        newY[0] = Math.round(event.getY(0));
        xChange[0] = Math.round(newX[0] - oldX[0]);
        yChange[0] = Math.round(newY[0] - oldY[0]);
        oldX[0] = newX[0];
        oldY[0] = newY[0];

        switch (numberOfFingers) {
        case 1:

            newLeft = rectangle.left + xChange[0];
            newTop = rectangle.top + yChange[0];
            newRight = rectangle.right + xChange[0];
            newBottom = rectangle.bottom + yChange[0];
            if(newLeft < 0 || newRight > metrics.widthPixels){
                newLeft = rectangle.left;
                newRight = rectangle.right;
            }
            if(newTop < 0 || newBottom > metrics.heightPixels){
                newTop = rectangle.top;
                newBottom = rectangle.bottom;
            }
            rectangle = new Rect(newLeft, newTop, newRight, newBottom);
            break;

        case 2:
            newX[1] = Math.round(event.getX(1));
            newY[1] = Math.round(event.getY(1));

            diffX =
                    Math.abs(Math.round(newX[1] - newX[0]))
                        - Math.abs(Math.round(oldX[1] - oldX[0]));
            diffY =
                    Math.abs(Math.round(newY[1] - newY[0]))
                        - Math.abs(Math.round(oldY[1] - oldY[0]));
            oldX[1] = newX[1];
            oldY[1] = newY[1];

            newLeft = rectangle.left - diffX / 2;
            newTop = rectangle.top - diffY / 2;
            newRight = rectangle.right + diffX / 2;
            newBottom = rectangle.bottom + diffY / 2;
            rectangle = new Rect(newLeft, newTop, newRight, newBottom);
            break;
        }
    }



}

这是我的错误日志:

10-31 04:45:17.663: E/AndroidRuntime(908): FATAL EXCEPTION: main
10-31 04:45:17.663: E/AndroidRuntime(908): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.les14/com.example.les14.MainActivity}: java.lang.NullPointerException
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.app.ActivityThread.access$600(ActivityThread.java:141)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.os.Looper.loop(Looper.java:137)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.app.ActivityThread.main(ActivityThread.java:5103)
10-31 04:45:17.663: E/AndroidRuntime(908):  at java.lang.reflect.Method.invokeNative(Native Method)
10-31 04:45:17.663: E/AndroidRuntime(908):  at java.lang.reflect.Method.invoke(Method.java:525)
10-31 04:45:17.663: E/AndroidRuntime(908):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
10-31 04:45:17.663: E/AndroidRuntime(908):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-31 04:45:17.663: E/AndroidRuntime(908):  at dalvik.system.NativeStart.main(Native Method)
10-31 04:45:17.663: E/AndroidRuntime(908): Caused by: java.lang.NullPointerException
10-31 04:45:17.663: E/AndroidRuntime(908):  at com.example.les14.MainActivity.onCreate(MainActivity.java:35)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.app.Activity.performCreate(Activity.java:5133)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
10-31 04:45:17.663: E/AndroidRuntime(908):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
10-31 04:45:17.663: E/AndroidRuntime(908):  ... 11 more
10-31 04:50:18.133: I/Process(908): Sending signal. PID: 908 SIG: 9
10-31 05:01:08.913: D/gralloc_goldfish(952): Emulator without GPU emulation detected.
4

1 回答 1

3

移动你setContentView的顶部。您应该在执行findViewById.

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

    MyView myView = new MyView(this);
    LinearLayout layout = (LinearLayout) findViewById(R.id.mainlayout);
    layout.addView(myView);
    myView.setOnTouchListener(this);
    //  radioGroup = (RadioGroup) findViewById(R.id.radioGroup1);

    getWindowManager().getDefaultDisplay().getMetrics(metrics);
   //radioGroup.setOnCheckedChangeListener(this);
}
于 2013-10-31T08:58:42.580 回答