Android模拟器：对不起 - 应用程序（app_name）意外停止。请再试一次

Question

我是Android的初学者，我正在制作一个使用RelativeLayout的Login UI应用程序，使用Eclipse + ADT使用Java代码。代码中没有错误，但是当我在模拟器上运行应用程序时，出现对​​话框 - 说 - 应用程序（app_name）意外停止。请再试一次。这是我的MainActivity.java代码：

package dg.relativelayoutincode; 

import android.os.Bundle; 
import android.app.Activity; 
import android.view.Menu; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.RelativeLayout; 
import android.widget.TextView; 
import android.widget.RelativeLayout.LayoutParams; 

public class MainActivity extends Activity { 
RelativeLayout main; 
EditText userNameValue, passwordValue; 
TextView message, userName, password; 
Button login; 
LayoutParams messageDimensions; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    init(); 
    createMessageTextView(); 
    main.addView(message, messageDimensions); 
    setContentView(main); 
} 

private void init() { 
    // TODO Auto-generated method stub 
    main = new RelativeLayout(this); 
    LayoutParams mainDimensions = new LayoutParams(
      LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT); 
    main.setLayoutParams(mainDimensions); 
    userNameValue = new EditText(this); 
    passwordValue = new EditText(this); 
    message = new TextView(this); 
    userName = new TextView(this); 
    password = new TextView(this); 
    login = new Button(this); 

} 

private void createMessageTextView() { 
    // TODO Auto-generated method stub 
    LayoutParams messageDimensions = new LayoutParams(
      LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); 
    messageDimensions.addRule(RelativeLayout.ALIGN_PARENT_LEFT); 
    message.setText("please login first"); 
    message.setLayoutParams(messageDimensions); 
}} 

这里是什么logcat的显示当我运行的应用程序：

08-08 22:24:57.498: D/AndroidRuntime(273): Shutting down VM 
08-08 22:24:57.498: W/dalvikvm(273): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 
08-08 22:24:57.528: E/AndroidRuntime(273): FATAL EXCEPTION: main 
08-08 22:24:57.528: E/AndroidRuntime(273): java.lang.RuntimeException: Unable to start activity ComponentInfo{dg.relativelayoutincode/dg.relativelayoutincode.MainActivity}: java.lang.NullPointerException 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.os.Handler.dispatchMessage(Handler.java:99) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.os.Looper.loop(Looper.java:123) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.app.ActivityThread.main(ActivityThread.java:4627) 
08-08 22:24:57.528: E/AndroidRuntime(273): at java.lang.reflect.Method.invokeNative(Native Method) 
08-08 22:24:57.528: E/AndroidRuntime(273): at java.lang.reflect.Method.invoke(Method.java:521) 
08-08 22:24:57.528: E/AndroidRuntime(273): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
08-08 22:24:57.528: E/AndroidRuntime(273): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
08-08 22:24:57.528: E/AndroidRuntime(273): at dalvik.system.NativeStart.main(Native Method) 
08-08 22:24:57.528: E/AndroidRuntime(273): Caused by: java.lang.NullPointerException 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.view.ViewGroup$LayoutParams.<init>(ViewGroup.java:3573) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.view.ViewGroup$MarginLayoutParams.<init>(ViewGroup.java:3723) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.widget.RelativeLayout$LayoutParams.<init>(RelativeLayout.java:1123) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.widget.RelativeLayout.generateLayoutParams(RelativeLayout.java:938) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.view.ViewGroup.addViewInner(ViewGroup.java:1975) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.view.ViewGroup.addView(ViewGroup.java:1865) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.view.ViewGroup.addView(ViewGroup.java:1845) 
08-08 22:24:57.528: E/AndroidRuntime(273): at dg.relativelayoutincode.MainActivity.onCreate(MainActivity.java:24) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
08-08 22:24:57.528: E/AndroidRuntime(273): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 
08-08 22:24:57.528: E/AndroidRuntime(273): ... 11 more 

请帮助。

Answer 1

尝试从

main.addView(message, messageDimensions); 

更改为

main.addView(message);