我正在尝试创建一个Android应用程序。我在其中创建了两个活动。在第一个活动用户登录时点击按钮，如果他勾选一个复选框让我登录，然后下次登出后他来到主页然后应用程序记住他的用户名并通过，如果他没有注销（在第二个活动中按下注销按钮）然后他们没有办法到达主页（第一个活动）。如果他没有退出，那么我想通过使用后退按钮或重新启动应用程序来阻止用户访问主页登录页面。
Runprogram-＆gt;输入登录信息 - ＆gt;下一页 - ＆gt;注销（运行正常） Runprogram-＆gt;输入登录信息 - ＆gt;下一页 - ＆gt;按下按钮按钮 - ＆gt;然后按退出按钮 - ＆gt; GOT ERROR（强制停止）
我的问题是当我按下按钮然后在第二个活动中点击退出按钮然后Emmulator显示按下意外关闭应用程序并强制停止。在logcat窗口中出现错误 -
ERROR/AndroidRuntime(348): FATAL EXCEPTION: main
java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=0, data=null} to activity {com.example/com.example.MyActivity}: java.lang.NullPointerException
我的主页（第一个活动代码是）=
package com.example;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.text.Editable;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.EditText;
public class MyActivity extends Activity
{
EditText editText,editText1;
CheckBox checkBox;
int Requestcd=1;
String str,str1,str2,struser;
SharedPreferences sharedPreferences;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
sharedPreferences = getSharedPreferences("computer" , MODE_PRIVATE);
str = sharedPreferences.getString("key", "hold");
if (str.equalsIgnoreCase("True") || str.equalsIgnoreCase("hold"))
{
editText=(EditText)findViewById(R.id.edit1);
editText1 =(EditText)findViewById(R.id.edit2);
checkBox = (CheckBox)findViewById(R.id.check1);
Button button = (Button)findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//To change body of implemented methods use File | Settings | File Templates.
if(checkBox.isChecked())
{
str1 = editText.getText().toString();
str2 = editText1.getText().toString();
SharedPreferences.Editor editor1 = sharedPreferences.edit();
editor1.putString("key1" , str1);
editor1.putString("key2" , str2);
editor1.commit();
}
struser = editText.getText().toString();
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString("key" , "false");
editor.putString("key5" , struser);
Intent intent = new Intent(MyActivity.this , Second.class );
startActivityForResult(intent , Requestcd);
editor.commit();
}
});
}
else
{
Intent intent = new Intent(MyActivity.this , Second.class );
startActivity(intent);
}
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data); //To change body of overridden methods use File | Settings | File Templates.
String str13 = data.getExtras().getString("txt");
String str14 = data.getExtras().getString("txt1");
editText.setText(str13);
editText1.setText(str14);
}
}
我的第二个活动（欢迎用户和注销按钮）代码是=
package com.example;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
/**
* Created by IntelliJ IDEA.
* User: devendra
* Date: 18/1/13
* Time: 9:57 AM
* To change this template use File | Settings | File Templates.
*/
public class Second extends Activity{
SharedPreferences sharedPreferences;
String str, str1,str2,str3;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main2);
sharedPreferences = getSharedPreferences("computer" , MODE_PRIVATE);
str3 = sharedPreferences.getString("key5" , "none");
str = sharedPreferences.getString("key" , "null");
Button button=(Button)findViewById(R.id.button2) ;
TextView textView =(TextView)findViewById(R.id.text1);
textView.setText("Welcome"+" " +str3);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//To change body of implemented methods use File | Settings | File Templates.
SharedPreferences.Editor editor1 = sharedPreferences.edit();
editor1.putString("key", "True");
str1 = sharedPreferences.getString("key1" , "Enter your username");
str2 = sharedPreferences.getString("key2","Enter your password");
editor1.remove("key1");
editor1.remove("key2");
Intent intent = new Intent();
intent.putExtra("txt",str1);
intent.putExtra("txt1",str2);
setResult(RESULT_OK, intent);
editor1.commit();
finish();
}
});
}
@Override
public void onBackPressed() {
super.onBackPressed(); //To change body of overridden methods use File | Settings | File Templates.
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString("key" , "false");
editor.commit();
System.out.println("you in back press");
if (str.equalsIgnoreCase("false"));
{
Intent intent2 = new Intent(Second.this , Second.class);
startActivity(intent2);
}
finish();
}
}
这是logcat窗口的完整错误描述
{01-24 16:24:02.810: DEBUG/dalvikvm(382): Debugger has detached; object registry had 1 entries
01-24 16:24:04.702: INFO/dalvikvm(68): Jit: resizing JitTable from 1024 to 2048
01-24 16:24:04.750: INFO/ActivityManager(68): Displayed com.example/.MyActivity: +2s89ms
01-24 16:24:09.940: DEBUG/dalvikvm(147): GC_EXPLICIT freed 125K, 50% free 2990K/5895K, external 5874K/7299K, paused 133ms
01-24 16:24:14.930: DEBUG/dalvikvm(242): GC_EXPLICIT freed 7K, 54% free 2544K/5511K, external 1625K/2137K, paused 92ms
01-24 16:24:20.030: DEBUG/dalvikvm(287): GC_EXPLICIT freed 503K, 55% free 2598K/5703K, external 1625K/2137K, paused 121ms
01-24 16:24:20.230: INFO/ActivityManager(68): Starting: Intent { cmp=com.example/.Second } from pid 390
01-24 16:24:20.850: INFO/ActivityManager(68): Displayed com.example/.Second: +563ms
01-24 16:24:22.800: WARN/KeyCharacterMap(390): No keyboard for id 0
01-24 16:24:22.810: WARN/KeyCharacterMap(390): Using default keymap: /system /usr/keychars/qwerty.kcm.bin
01-24 16:24:22.820: INFO/System.out(390): you in back press
01-24 16:24:22.830: INFO/ActivityManager(68): Starting: Intent { cmp=com.example/.Second } from pid 390
01-24 16:24:22.830: WARN/ActivityManager(68): Duplicate finish request for HistoryRecord{406b1eb0 com.example/.Second}
01-24 16:24:23.520: INFO/ActivityManager(68): Displayed com.example/.Second: +673ms
01-24 16:24:26.340: DEBUG/AndroidRuntime(390): Shutting down VM
01-24 16:24:26.340: WARN/dalvikvm(390): threadid=1: thread exiting with uncaught exception (group=0x40015560)
01-24 16:24:26.370: ERROR/AndroidRuntime(390): FATAL EXCEPTION: main
java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1, result=0, data=null} to activity {com.example/com.example.MyActivity}: java.lang.NullPointerException
at android.app.ActivityThread.deliverResults(ActivityThread.java:2532)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:2574)
at android.app.ActivityThread.access$2000(ActivityThread.java:117)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:961)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:3683)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.MyActivity.onActivityResult(MyActivity.java:69)
at android.app.Activity.dispatchActivityResult(Activity.java:3908)
at android.app.ActivityThread.deliverResults(ActivityThread.java:2528)
... 11 more
01-24 16:24:26.380: WARN/ActivityManager(68): Force finishing activity com.example/.MyActivity
01-24 16:24:26.920: WARN/ActivityManager(68): Activity pause timeout for HistoryRecord{4061a9d0 com.example/.MyActivity}
01-24 16:24:33.801: DEBUG/dalvikvm(320): GC_EXPLICIT freed 323K, 54% free 2539K/5511K, external 1625K/2137K, paused 104ms
01-24 16:24:38.356: WARN/ActivityManager(68): Activity destroy timeout for HistoryRecord{4061a9d0 com.example/.MyActivity}
01-24 16:24:38.702: WARN/ActivityManager(68): Activity destroy timeout for HistoryRecord{406ef998 com.example/.Second}
01-24 16:24:50.600: INFO/Process(390): Sending signal. PID: 390 SIG: 9
01-24 16:24:51.310: INFO/ActivityManager(68): Process com.example (pid 390) has died.
01-24 16:24:51.320: INFO/WindowManager(68): WIN DEATH: Window{4069f500 com.example/com.example.MyActivity paused=false}
01-24 16:24:51.340: ERROR/InputDispatcher(68): channel '4055da70 com.example/com.example.Second (server)' ~ Consumer closed input channel or an error occurred. events=0x8
01-24 16:24:51.340: ERROR/InputDispatcher(68): channel '4055da70 com.example/com.example.Second (server)' ~ Channel is unrecoverably broken and will be disposed!
01-24 16:24:51.450: INFO/WindowManager(68): WIN DEATH: Window{4055da70 com.example/com.example.Second paused=false}}
答案 0 :(得分：2)
您有两个不同的值来确定如何处理对startActivityForResult()的调用。 On是标识requestCode来电的startActivityForResult()，因为您可能有多个。{1}}。您使用Requestcd作为标识符。
第二个是resultCode，它可以让您了解结果的状态。如果其值为RESULT_OK，则结果已在已启动的活动中成功设置。如果按后退按钮，则值为RESULT_CANCELED。
在您的情况下，您需要检查这两个值，并仅在requestCode和resultCode符合预期时执行。如果值不同，你应该考虑做一些事情来对此做出反应。可能性是通知用户他应该执行的任务（例如：选择图片）被取消。
尝试使用以下代码仅在设置结果时才读取意图数据。
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == Requestcd) {
if (resultCode == RESULT_OK) {
String str13 = data.getExtras().getString("txt");
String str14 = data.getExtras().getString("txt1");
editText.setText(str13);
editText1.setText(str14);
}
}
}