OnClickListener 的 NullPointerException android Java

Question

我很抱歉问这个问题，但是现在 2 个小时我找不到任何方法来解决这个问题： **问题：** 我已经设置了一个 canvas 区域（我在其中绘制了一个可绘制的图形）和 canvas 区域下方的一个按钮。在我的 AnimatedView class 中，我想找到按钮并给它一个 onClickListener，但它 returns 一个 NullPointerException。

我的activity_main.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_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"
android:orientation="vertical"
android:background="#000000">

<com.example.julle.bounce.AnimatedView
    android:id="@+id/anim_view"
    android:layout_height="300dp"
    android:layout_width="fill_parent"/>
<Button
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_below="@+id/anim_view"
    android:id="@+id/button_jump"
    android:clickable="true"
    android:text="Jump"/>

我的 AnimatedView.java 代码：

    package com.example.julle.bounce;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.drawable.BitmapDrawable;
import android.os.Handler;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

public class AnimatedView extends ImageView{
    private Context mContext;
    int x = -1;
    int y = -1;
    private int xVelocity = 10;
    private int yVelocity = 5;
    private Handler h;
    private final int FRAME_RATE = 30;
    boolean jump=false;

    public AnimatedView(Context context, AttributeSet attrs)  {
        super(context, attrs);
        mContext = context;
        final Button button = (Button) findViewById(R.id.button_jump);
        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                jump=true;
            }
        });
        h = new Handler();
    }
    private Runnable r = new Runnable() {
        @Override
        public void run() {
            invalidate();

        }
    };
    protected void onDraw(Canvas c) {
        BitmapDrawable ball = (BitmapDrawable) mContext.getResources().getDrawable(R.drawable.ball);
        if(jump==true) {
            if (y < 0) {
                y = this.getHeight() / 2;
            } else {
                y += yVelocity;
            }
            jump=false;
        }else{
            y= this.getHeight()/2;
        }

        c.drawBitmap(ball.getBitmap(), x, y, null);
        h.postDelayed(r, FRAME_RATE);
    }
}

和我的 MainActivity：

package com.example.julle.bounce;

import ...


public class MainActivity extends ActionBarActivity {

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

}

我相信我已经意识到问题所在：按钮存在于 MainActivity class 但不存在于我的 AnimatedView class 中。尽管这可能非常简单，但我不确定如何解决。感谢大家的回复！

抱歉，完全忘记我更改了代码。 AnimatedView 已更新：给出 NullPointException 的行是 AnimatedView 中的第 26 行：button.setOnClickListener...

logcat:

02-24 14:47:32.005  31934-31934/com.example.julle.bounce E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.julle.bounce/com.example.julle.bounce.MainActivity}: android.view.InflateException: Binary XML file line #13: Error inflating class com.example.julle.bounce.AnimatedView
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
            at android.app.ActivityThread.access0(ActivityThread.java:140)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4921)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: android.view.InflateException: Binary XML file line #13: Error inflating class com.example.julle.bounce.AnimatedView
            at android.view.LayoutInflater.createView(LayoutInflater.java:613)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:687)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:746)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
            at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:228)
            at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
            at com.example.julle.bounce.MainActivity.onCreate(MainActivity.java:23)
            at android.app.Activity.performCreate(Activity.java:5206)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
            at android.app.ActivityThread.access0(ActivityThread.java:140)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4921)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.reflect.InvocationTargetException
            at java.lang.reflect.Constructor.constructNative(Native Method)
            at java.lang.reflect.Constructor.newInstance(Constructor.java:417)
            at android.view.LayoutInflater.createView(LayoutInflater.java:587)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:687)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:746)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
            at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:228)
            at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
            at com.example.julle.bounce.MainActivity.onCreate(MainActivity.java:23)
            at android.app.Activity.performCreate(Activity.java:5206)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
            at android.app.ActivityThread.access0(ActivityThread.java:140)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4921)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.julle.bounce.AnimatedView.<init>(AnimatedView.java:26)
            at java.lang.reflect.Constructor.constructNative(Native Method)
            at java.lang.reflect.Constructor.newInstance(Constructor.java:417)
            at android.view.LayoutInflater.createView(LayoutInflater.java:587)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:687)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:746)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:489)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:396)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:352)
            at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:228)
            at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
            at com.example.julle.bounce.MainActivity.onCreate(MainActivity.java:23)
            at android.app.Activity.performCreate(Activity.java:5206)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
            at android.app.ActivityThread.access0(ActivityThread.java:140)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:4921)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

您可以将对按钮的引用从主 activity 传递到 AnimatedView class。

package com.example.julle.bounce;
import ...
public class MainActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btn = (Button)findViewByID(R.id.button_jump);    
        AnimatedView av = (AnimatedView)findViewByID(R.id.anm_view);
        av.setJumpButton(btn);
    }

}

您需要在 AnimatedView class 中添加 setJumpButton 方法。

OnClickListener 的 NullPointerException android Java

NullPointerException for OnClickListener android Java

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