Question

如果已经查看，我有问题显示吐司而不是其他吐司。我有两个活动，在第一个活动toast中显示，我有这个代码：

@Override
 protected void onCreate(Bundle savedInstanceState) {
 // TODO Auto-generated method stub
 super.onCreate(savedInstanceState);
 setContentView(R.layout.q_050);
 String str = getIntent().getStringExtra("sent");
// at this line--> if(str.equals("activity_two")){
     Toast.makeText(getApplicationContext(), getApplicationContext().getString(R.string.app_name), Toast.LENGTH_SHORT).show();
 }
 else{
     Toast.makeText(getApplicationContext(), getApplicationContext().getString(R.string.checkpoint), Toast.LENGTH_SHORT).show();
 }

在后退按钮中的第二个活动中我包含了这个：

  Button b3 = (Button)findViewById(R.id.b3);
                b3.setOnClickListener(new Button.OnClickListener() {  
                       public void onClick(View v){

                           Intent myIntentActivity1 = new Intent(Q_051.this,Q_050.class);
                           myIntentActivity1.putExtra("sent", "activity_two");
                           startActivity(myIntentActivity1);

和logcat中的问题是：

 11-09 16:29:51.920: E/AndroidRuntime(1510): FATAL EXCEPTION: main
11-09 16:29:51.920: E/AndroidRuntime(1510): java.lang.RuntimeException: Unable to start activity ComponentInfo{org.quizcelebrita/org.quizcelebrita.Q_050}: java.lang.NullPointerException
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.app.ActivityThread.access$600(ActivityThread.java:140)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.os.Looper.loop(Looper.java:137)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.app.ActivityThread.main(ActivityThread.java:4898)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at java.lang.reflect.Method.invokeNative(Native Method)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at java.lang.reflect.Method.invoke(Method.java:511)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at dalvik.system.NativeStart.main(Native Method)
11-09 16:29:51.920: E/AndroidRuntime(1510): Caused by: java.lang.NullPointerException
11-09 16:29:51.920: E/AndroidRuntime(1510):     at org.quizcelebrita.Q_050.onCreate(Q_050.java:32)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.app.Activity.performCreate(Activity.java:5206)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1083)
11-09 16:29:51.920: E/AndroidRuntime(1510):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064)
11-09 16:29:51.920: E/AndroidRuntime(1510):     ... 11 more

检测到问题的行是：

   if(str.equals("activity_two")){

Answer 1

更改

 Bundle value = getIntent().getExtras();
 String str= value.getString("sent").toString();

在

String str = getIntent().getStringExtra("sent");

另外，Java中的字符串比较应该通过equals方法

来执行

if(str.equals("activity_two"))

Answer 2

您在提到的if条件中遇到空指针异常尝试调试您的应用程序并在此行上设置断点： -

String str = getIntent().getStringExtra("sent");

检查str是否获得任何值。我猜它没有收到任何字符串，这就是它显示空指针异常

的原因

Android：无法显示祝酒词

2 个答案: