android setText崩溃我的应用程序

Question

我在Android 16（4.1）应用程序上使用setText()方法时出现问题。我试图编程任何东西到TextView tvopis（这里只是一些测试字符串，后来我打算从意图把那里的字符串）。 当我打开活动opis时，应用程序崩溃。如果我评论setText()部分，一切工作正常。

这里的Java代码

package com.example.pierwszyandroid; 

import android.app.Activity; 
import android.app.ActionBar; 
import android.app.Fragment; 
import android.os.Bundle; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.TextView; 
import android.os.Build; 

public class OpisActivity extends Activity { 

    public TextView tvopis; 
    String txt; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_opis); 
     tvopis = (TextView) findViewById(R.id.tvotest); 

     tvopis.setText("txt test"); 


     if (savedInstanceState == null) { 
      getFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit(); 
     } 
    } 

这里的fragment_opis.xml这项活动：

<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:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context="com.example.pierwszyandroid.OpisActivity$PlaceholderFragment" > 

    <TextView 
     android:id="@+id/tvotest" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_centerVertical="true" 
     android:text="@string/hello_world" /> 

</RelativeLayout> 

，这是activity_opis.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:id="@+id/container" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    tools:context="com.example.pierwszyandroid.OpisActivity" 
    tools:ignore="MergeRootFrame" /> 

和这里的logcat的错误消息：

04-18 10:44:59.665: I/Choreographer(723): Skipped 206 frames! The application may be doing too much work on its main thread. 
04-18 10:46:34.016: I/Choreographer(723): Skipped 41 frames! The application may be doing too much work on its main thread. 
04-18 10:46:34.135: D/AndroidRuntime(723): Shutting down VM 
04-18 10:46:34.135: W/dalvikvm(723): threadid=1: thread exiting with uncaught exception (group=0x2bc9a300) 
04-18 10:46:34.155: E/AndroidRuntime(723): FATAL EXCEPTION: main 
04-18 10:46:34.155: E/AndroidRuntime(723): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.pierwszyandroid/com.example.pierwszyandroid.OpisActivity}: java.lang.NullPointerException 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.app.ActivityThread.access$600(ActivityThread.java:130) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.os.Handler.dispatchMessage(Handler.java:99) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.os.Looper.loop(Looper.java:137) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.app.ActivityThread.main(ActivityThread.java:4745) 
04-18 10:46:34.155: E/AndroidRuntime(723): at java.lang.reflect.Method.invokeNative(Native Method) 
04-18 10:46:34.155: E/AndroidRuntime(723): at java.lang.reflect.Method.invoke(Method.java:511) 
04-18 10:46:34.155: E/AndroidRuntime(723): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
04-18 10:46:34.155: E/AndroidRuntime(723): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
04-18 10:46:34.155: E/AndroidRuntime(723): at dalvik.system.NativeStart.main(Native Method) 
04-18 10:46:34.155: E/AndroidRuntime(723): Caused by: java.lang.NullPointerException 
04-18 10:46:34.155: E/AndroidRuntime(723): at com.example.pierwszyandroid.OpisActivity.onCreate(OpisActivity.java:25) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.app.Activity.performCreate(Activity.java:5008) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 
04-18 10:46:34.155: E/AndroidRuntime(723): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 
04-18 10:46:34.155: E/AndroidRuntime(723): ... 11 more 

任何帮助将非常感激，因为我找不到任何已发布的类似问题的答案。

Answer 1

布局您已经设置错误您的布局在onCreate()方法。您TextView驻留在布局fragment_opis.xml内，而您已将布局设置为setContentView(R.layout.activity_opis);。

您setContentView(R.layout.activity_opis);线只要改变

为以下

setContentView(R.layout. fragment_opis); 

Answer 2

如果您查看log cat，当您尝试将文本设置为文本视图（OpisActivity中的第25行）时，您会看到您有空指针异常。

这意味着在布局中找不到txt视图，因此无法初始化。由于您的textview位于片段中，因此您必须先将片段添加到布局，然后查找该视图。

解决您的问题，该片段初始化后移动findById和方法的setText在onCreate方法，像这样：

protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_opis); 

    if (savedInstanceState == null) { 
     getFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit(); 
    } 

    tvopis = (TextView) findViewById(R.id.tvotest); 
    tvopis.setText("txt test"); 
} 

Answer 3

您的应用程序崩溃，因为你的TextView tvotest属于fragment_opis.xml布局和你必须将activity_opis.xml文件设置为您的活动。

所以初始化PlaceholderFragment()先初始化您的TextView tvotest或更改像

setContentView(R.layout.fragment_opis.xm) 

Answer 4

改变这种setContentView(R.layout.activity_opis);

这个

setContentView(R.layout.fragment_opis.xml);