从Android中的LinearLayout中删除视图时出现异常

Posted 2023-02-26

【中文标题】从Android中的LinearLayout中删除视图时出现异常

【英文标题】：Exception while removing a view from a LinearLayout in Android

【发布时间】：2011-07-03 01:00:43

【问题描述】：

我试图在将自定义视图从 LinearLayout 容器中删除之前对其进行动画处理。只有我不断收到 NullPointerException，我无法追踪到任何特定的地方。

当我添加两个视图并删除第一个视图时会发生异常。

我的代码是：

protected void onCreate(Bundle savedInstanceState) 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.form_alg);
    fadeInAnimation = AnimationUtils.loadAnimation(getApplicationContext(),
            R.anim.witness_fade_in);

    list = (LinearLayout) this.findViewById(R.id.alg_list_getuigen);

    addWitness = (ImageButton) this
            .findViewById(R.id.alg_getuige_toevoegen);
    addWitness.setOnClickListener(new OnClickListener() 
        @Override
        public void onClick(View v) 
            final View w = View.inflate(getApplicationContext(),
                    R.layout.form_getuige, null);

            ImageButton button = (ImageButton) w
                    .findViewById(R.id.getuige_verwijderen);
            button.setOnClickListener(new android.view.View.OnClickListener() 

                @Override
                public void onClick(View v) 
                    Log.d(TAG, "deleteView");
                    Animation fadeOutAnimation = AnimationUtils
                            .loadAnimation(getApplicationContext(),
                                    R.anim.witness_fade_out);
                    fadeOutAnimation
                            .setAnimationListener(new AnimationListener() 
                                @Override
                                public void onAnimationEnd(
                                        Animation animation) 
                                    list.removeView(w);
                                    list.invalidate();
                                

                                @Override
                                public void onAnimationRepeat(
                                        Animation animation) 
                                

                                @Override
                                public void onAnimationStart(
                                        Animation animation) 
                                
                            );
                    w.setVisibility(View.VISIBLE);
                    w.startAnimation(fadeOutAnimation);
                    w.setVisibility(View.INVISIBLE);
                
            );
            Log.d(TAG, "addView");

            w.setVisibility(View.INVISIBLE);
            list.addView(w);
            w.startAnimation(fadeInAnimation);
            w.setVisibility(View.VISIBLE);
            list.invalidate();
        

    );

这是堆栈跟踪：

07-03 03:17:30.335: WARN/dalvikvm(343): threadid=1: thread exiting with uncaught exception (group=0x40015560)
07-03 03:17:30.365: ERROR/AndroidRuntime(343): FATAL EXCEPTION: main
07-03 03:17:30.365: ERROR/AndroidRuntime(343): java.lang.NullPointerException
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1372)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.drawChild(ViewGroup.java:1644)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.View.draw(View.java:6986)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.widget.FrameLayout.draw(FrameLayout.java:357)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.widget.ScrollView.draw(ScrollView.java:1409)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.drawChild(ViewGroup.java:1646)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.drawChild(ViewGroup.java:1644)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.View.draw(View.java:6883)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.widget.FrameLayout.draw(FrameLayout.java:357)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.drawChild(ViewGroup.java:1646)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.drawChild(ViewGroup.java:1644)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.View.draw(View.java:6883)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.widget.FrameLayout.draw(FrameLayout.java:357)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1862)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewRoot.draw(ViewRoot.java:1522)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewRoot.performTraversals(ViewRoot.java:1258)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1859)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.os.Looper.loop(Looper.java:123)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at android.app.ActivityThread.main(ActivityThread.java:3683)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at java.lang.reflect.Method.invokeNative(Native Method)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at java.lang.reflect.Method.invoke(Method.java:507)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
07-03 03:17:30.365: ERROR/AndroidRuntime(343):     at dalvik.system.NativeStart.main(Native Method)

【问题讨论】：

能否请您发布完整的堆栈跟踪并指出跟踪第一行中引用的行号？谢谢！

NullPointerException 通常意味着您试图在一个为空的对象上调用一个方法。在调用 list.removeView(w) 之类的东西之前，您应该始终检查是否为 list != null。

【参考方案1】：

我遇到了同样的问题。您必须使用 Handler 来执行修改 UI 的代码（在本例中为 removeView()）。我会添加一个 Handler 字段并在您的 onCreate() 方法中构造它。然后，在 onAnimationEnd() 中，这样做：

fHandler.post(new Runnable() 
    @Override
    public void run() 
        list.removeView(w);
        list.invalidate();
    

【讨论】：

你能解释一下为什么吗？是否有关于此的 Android 文档的链接？

@kolistivra，类似的问题：***.com/questions/5569267/…。答：“当你在animationEnd中改变视图层次时，Android会抛出异常”。但是为什么 - 我不知道。

【参考方案2】：

要删除布局的所有子元素，然后添加新子元素，请查找以下代码

if (linearLayout.getChildCount() > 0)
            
                linearLayout.removeAllViewsInLayout();
                linearLayout.invalidate();