java - Android setImageResource 导致应用程序崩溃

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已关闭。这个问题是 not reproducible or was caused by typos 。目前不接受答案。

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这个问题是由拼写错误或无法再重现的问题引起的。虽然类似的问题可能是 on-topic在这里，这个问题的解决方式不太可能帮助 future 的读者。

已关闭 8 年前。

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首先，我对 Android 编程还很陌生，所以这个错误很可能是我没有注意到的非常简单的事情。但每当我打开我的简单应用程序时，它都会以图像开始。当我滑动时，它应该更改为不同的图像，但应用程序崩溃了。有什么想法吗？

这是我的java代码

package example.course.bananapeeler;
import android.gesture.Gesture;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.TextView;
import android.widget.ImageView;
import android.view.MotionEvent;
import android.view.GestureDetector;
import android.support.v4.view.GestureDetectorCompat;

public class MainActivity extends ActionBarActivity implements GestureDetector.OnGestureListener,
        GestureDetector.OnDoubleTapListener{

    private ImageView mainPic;
    private GestureDetectorCompat gestureDetector;
    private int moneyPerSecond;

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

        this.gestureDetector = new GestureDetectorCompat(this, this);
        gestureDetector.setOnDoubleTapListener(this);

        //ImageView mainPic = (ImageView)findViewById(R.id.mainPic);
        ImageView mainPic = (ImageView)findViewById(R.id.mainPic);
        }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent motionEvent) {

        return false;
    }

    @Override
    public boolean onDoubleTap(MotionEvent motionEvent) {

        return false;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent motionEvent) {

        return false;
    }

    @Override
    public boolean onDown(MotionEvent motionEvent) {
        return true;
    }

    @Override
    public void onShowPress(MotionEvent motionEvent) {


    }

    @Override
    public boolean onSingleTapUp(MotionEvent motionEvent) {

        return false;
    }

    @Override
    public boolean onScroll(MotionEvent motionEvent, MotionEvent motionEvent2, float v, float v2) {

        return false;
    }

    @Override
    public void onLongPress(MotionEvent motionEvent) {

    }

    @Override
    public boolean onFling(MotionEvent motionEvent, MotionEvent motionEvent2, float v, float v2) {
        /*
        ImageView img = new ImageView(this);
        findViewById(R.id.mainPic);
        */
        mainPic.setImageResource(R.drawable.peeledbanana);

        return true;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        this.gestureDetector.onTouchEvent(event);
        return super.onTouchEvent(event);

    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

xml 文件:

<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"><![CDATA[


/"peeledbanana";
    android:id="@+id/imageView"
    android:layout_centerVertical="true"
    android:layout_centerHorizontal="true" />
]]>

<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/mainPic"
    android:layout_centerVertical="true"
    android:layout_centerHorizontal="true"
    android:src="@drawable/mainbanana"
    android:contentDescription="@string/mainPic" />
</RelativeLayout>

不知道为什么语法文件的格式很奇怪。这是导致崩溃的原因吗？

Logcat 错误

05-13 17:16:47.329 2333-2333/example.course.bananapeeler E/InputEventReceiver﹕ Exception dispatching input event. 05-13 17:16:47.329 2333-2333/example.course.bananapeeler E/MessageQueue-JNI﹕ Exception in MessageQueue callback: handleReceiveCallback 05-13 17:16:47.339
2333-2333/example.course.bananapeeler E/MessageQueue-JNI﹕ java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference at example.course.bananapeeler.MainActivity.onFling(MainActivity.java:88) at android.view.GestureDetector.onTouchEvent(GestureDetector.java:620) at android.support.v4.view.GestureDetectorCompat$GestureDetectorCompatImplJellybeanMr2.onTouchEvent(GestureDetectorCompat.java:475) at android.support.v4.view.GestureDetectorCompat.onTouchEvent(GestureDetectorCompat.java:538) at example.course.bananapeeler.MainActivity.onTouchEvent(MainActivity.java:102) at android.app.Activity.dispatchTouchEvent(Activity.java:2869) at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:59) at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2529) at android.view.View.dispatchPointerEvent(View.java:9180) at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4734) at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4572) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4096) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4149) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4115) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4229) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4123) at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4286) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4096) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4149) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4115) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4123) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4096) at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6600) at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6484) at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6455) at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6690) at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185) at android.os.MessageQueue.nativePollOnce(Native Method) at android.os.MessageQueue.next(MessageQueue.java:143) at android.os.Looper.loop(Looper.java:130) at android.app.ActivityThread.main(ActivityThread.java:5972) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1388) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1183) 05-13 17:16:47.339 2333-2333/example.course.bananapeeler D/AndroidRuntime﹕ Shutting down VM 05-13 17:16:47.339
2333-2333/example.course.bananapeeler E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: example.course.bananapeeler, PID: 2333 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ImageView.setImageResource(int)' on a null object reference at example.course.bananapeeler.MainActivity.onFling(MainActivity.java:88) at android.view.GestureDetector.onTouchEvent(GestureDetector.java:620) at android.support.v4.view.GestureDetectorCompat$GestureDetectorCompatImplJellybeanMr2.onTouchEvent(GestureDetectorCompat.java:475) at android.support.v4.view.GestureDetectorCompat.onTouchEvent(GestureDetectorCompat.java:538) at example.course.bananapeeler.MainActivity.onTouchEvent(MainActivity.java:102) at android.app.Activity.dispatchTouchEvent(Activity.java:2869) at android.support.v7.internal.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:59) at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2529) at android.view.View.dispatchPointerEvent(View.java:9180) at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4734) at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4572) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4096) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4149) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4115) at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4229) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4123) at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4286) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4096) at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4149) at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4115) at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4123) at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4096) at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6600) at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6484) at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6455) at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6690) at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185) at android.os.MessageQueue.nativePollOnce(Native Method) at android.os.MessageQueue.next(MessageQueue.java:143) at android.os.Looper.loop(Looper.java:130) at android.app.ActivityThread.main(ActivityThread.java:5972) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1388) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1183)

Answer 1

您正在本地初始化 mainPic 而不是类变量。

改变

ImageView mainPic = (ImageView)findViewById(R.id.mainPic);

至

mainPic = (ImageView)findViewById(R.id.mainPic);