Android：应用在启动新活动时崩溃

时间：2013-07-05 19:08:59

标签： android crash textview

基本上，我想开始一个活动，打印出输入字符串和一个图像。

在activity_display_message.xml中：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical" >

      <TextView 
            android:text="@+id/textView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            />

        <ImageView
        android:id="@+id/imageView2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:src="@drawable/serious" />    


</LinearLayout>

这是OnCreate（）中的代码：

    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_display_message);  
    Intent intent = getIntent();

    String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

    ImageView image2 = (ImageView) findViewById(R.id.imageView2);


    // Create the text view

    TextView textView = (TextView)findViewById(R.id.textView);
    //textView.setTextSize(20);

    textView.setText(message);
    // Set the text view as the activity layout   


    // Show the Up button in the action bar.
    setupActionBar();
}

这段代码有什么问题吗？

编辑：不确定如何获得堆栈跟踪，但我刚刚在Catlog中找到了这些行：

07-05 12:26:53.677: E/AppsCustomizePagedView(611): Widget ComponentInfo{com.th.android.widget.gTabsimiClock/com.th.android.widget.gTabsimiClock.GTabsimiClock5x1} can not fit on this device (736, 144)
07-05 12:26:53.692: E/AppsCustomizePagedView(611): Widget ComponentInfo{at.abraxas.powerwidget.free/at.abraxas.powerwidget.free.SettingsAppWidgetProvider_5} can not fit on this device (760, 80)
07-05 12:26:57.958: E/AudioCache(131): Error 1, -1004 occurred
07-05 12:26:58.146: E/AudioCache(131): Error 1, -1004 occurred
07-05 12:26:58.630: E/AudioCache(131): Error 1, -1004 occurred
07-05 12:27:07.833: E/AudioCache(131): Heap size overflow! req size 1052672, max size: 1048576

这是堆栈跟踪吗？

07-05 12:41:10.058: E/TAG(22474): STACKTRACE
07-05 12:41:10.058: E/TAG(22474): java.lang.NullPointerException
07-05 12:41:10.058: E/TAG(22474):   at com.example.myfirstapp.DisplayMessageActivity.onCreate(DisplayMessageActivity.java:38)
07-05 12:41:10.058: E/TAG(22474):   at android.app.Activity.performCreate(Activity.java:5104)
07-05 12:41:10.058: E/TAG(22474):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-05 12:41:10.058: E/TAG(22474):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
07-05 12:41:10.058: E/TAG(22474):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-05 12:41:10.058: E/TAG(22474):   at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-05 12:41:10.058: E/TAG(22474):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-05 12:41:10.058: E/TAG(22474):   at android.os.Handler.dispatchMessage(Handler.java:99)
07-05 12:41:10.058: E/TAG(22474):   at android.os.Looper.loop(Looper.java:137)
07-05 12:41:10.058: E/TAG(22474):   at android.app.ActivityThread.main(ActivityThread.java:5041)
07-05 12:41:10.058: E/TAG(22474):   at java.lang.reflect.Method.invokeNative(Native Method)
07-05 12:41:10.058: E/TAG(22474):   at java.lang.reflect.Method.invoke(Method.java:511)
07-05 12:41:10.058: E/TAG(22474):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-05 12:41:10.058: E/TAG(22474):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-05 12:41:10.058: E/TAG(22474):   at dalvik.system.NativeStart.main(Native Method)

在运行时崩溃时的堆栈跟踪:(上面的那个是通过try / catch获得的）

07-05 12:52:24.386: E/AndroidRuntime(25496): FATAL EXCEPTION: main
07-05 12:52:24.386: E/AndroidRuntime(25496): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myfirstapp/com.example.myfirstapp.DisplayMessageActivity}: java.lang.NullPointerException
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.os.Looper.loop(Looper.java:137)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.app.ActivityThread.main(ActivityThread.java:5041)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at java.lang.reflect.Method.invokeNative(Native Method)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at java.lang.reflect.Method.invoke(Method.java:511)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at dalvik.system.NativeStart.main(Native Method)
07-05 12:52:24.386: E/AndroidRuntime(25496): Caused by: java.lang.NullPointerException
07-05 12:52:24.386: E/AndroidRuntime(25496):    at com.example.myfirstapp.DisplayMessageActivity.onCreate(DisplayMessageActivity.java:38)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.app.Activity.performCreate(Activity.java:5104)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
07-05 12:52:24.386: E/AndroidRuntime(25496):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
07-05 12:52:24.386: E/AndroidRuntime(25496):    ... 11 more

消息不为空。当我将OnCreate更改为以下时，将打印消息:(当然，不是图像）

// Create the text view

//TextView textView = (TextView)findViewById(R.id.textView);
TextView textView = new TextView(this);
textView.setTextSize(20);

textView.setText(message);
setContentView(textView);

答案：发现错误：android：text =“@ + id / textView”。应该是android：id，而不是android：text ...

但是谢谢大家的帮助。你们为像我这样的初学者提供了更好的编程体验。

4 个答案:

答案 0 :(得分：6)

您需要先将内容设置为活动。

您可以findViewById设置为活动的当前视图层次结构。由于您尚未将内容设置为活动，因此如果您尝试初始化视图，则会获得NullPointerException。

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_display_message); 
String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
ImageView image2 = (ImageView) findViewById(R.id.imageView2);
TextView textView = (TextView)findViewById(R.id.textView);
textView.setTextSize(20);
textView.setText(message);
....
}

编辑：

由于Squonk评论setText(CharSequence text)检查空

这

http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.2.2_r1/android/widget/TextView.java#TextView.setText%28java.lang.CharSequence%2Candroid.widget.TextView.BufferType%29

实现类似于

3561    private void setText(CharSequence text, BufferType type,
3562                         boolean notifyBefore, int oldlen) {
3563        if (text == null) { // checking for null
3564            text = ""; 
3565        }   
        .....

因此第38行是textView.setText(message)，导致NPE。因此textView未初始化，导致NPE。

继续更新和Squonk评论

如果textview文件已损坏，

R.id可以为null bcoz指定错误（或无效）R.java OR。在后一种情况下，使用Project - ＆gt;清洁应该解决问题。

也是这个

android:text="@+id/textView" // this is actually setting text to textview.

你错过了

android:id="@+id/textView" // textview id attribute missing

当你尝试初始化

时 
TextView textView = (TextView)findViewById(R.id.textView);
// there is no textview with id  textView which caused NPE

答案 1 :(得分：1)

应在创建Imageview对象之前调用setContentView。

答案 2 :(得分：0)

put setContentView（R.layout.activity_display_message）; onCreate方法顶部的行。

    @Override
    public void onCreate() {
    super.onCreate();
    setContentView(R.layout.activity_display_message); 

    ......
    rest code

    }

答案 3 :(得分：0)

您是否在清单文件中声明了您的活动？请检查一下。

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