将变量从活动传递到另一个

时间：2014-03-12 22:04:34

标签： android android-intent

我尝试将一个变量从一个活动发送到另一个但我得到一个错误。我正在使用它，因为我想将一些菜单的一些数据发送到另一个活动，然后根据数据修改文本视图接收。我只附加了一个我要发送的信息，即标题。 我已经附上了我的活动和LogCat错误：

MainActivity 

        Bundle bundle= new Bundle();
        bundle.putString("Title", lessons_titles[position]);                                  

        Intent intent = new Intent(context, Example1.class);

        intent.putExtras(bundle);
        context.startActivity(intent);

传递活动 

    Bundle bundle = getIntent().getExtras();
    String title = bundle.getString("Title");                           
    title_view.setText(title);

LogCat错误 

03-12 17:18:31.529: E/AndroidRuntime(1873): FATAL EXCEPTION: main
03-12 17:18:31.529: E/AndroidRuntime(1873): java.lang.RuntimeException: Unable to    instantiate activity ComponentInfo{com.example.test/com.example.test.Example1}:   java.lang.NullPointerException
03-12 17:18:31.529: E/AndroidRuntime(1873):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at  android.os.Handler.dispatchMessage(Handler.java:99)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at android.os.Looper.loop(Looper.java:137)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at android.app.ActivityThread.main(ActivityThread.java:5103)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at java.lang.reflect.Method.invokeNative(Native Method)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at java.lang.reflect.Method.invoke(Method.java:525)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at dalvik.system.NativeStart.main(Native Method)
03-12 17:18:31.529: E/AndroidRuntime(1873): Caused by: java.lang.NullPointerException
03-12 17:18:31.529: E/AndroidRuntime(1873):     at android.app.Activity.findViewById(Activity.java:1853)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at com.example.test.Example1.<init>(Example1.java:10)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at java.lang.Class.newInstanceImpl(Native Method)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at java.lang.Class.newInstance(Class.java:1130)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
03-12 17:18:31.529: E/AndroidRuntime(1873):     at    android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
03-12 17:18:31.529: E/AndroidRuntime(1873):     ... 11 more
03-12 17:21:55.112: E/AndroidRuntime(2031): FATAL EXCEPTION: main
03-12 17:21:55.112: E/AndroidRuntime(2031): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.test/com.example.test.Example1}: java.lang.NullPointerException
03-12 17:21:55.112: E/AndroidRuntime(2031):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at  android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at android.os.Looper.loop(Looper.java:137)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at android.app.ActivityThread.main(ActivityThread.java:5103)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at java.lang.reflect.Method.invokeNative(Native Method)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at java.lang.reflect.Method.invoke(Method.java:525)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at dalvik.system.NativeStart.main(Native Method)
03-12 17:21:55.112: E/AndroidRuntime(2031): Caused by: java.lang.NullPointerException
03-12 17:21:55.112: E/AndroidRuntime(2031):     at   android.app.Activity.findViewById(Activity.java:1853)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at com.example.test.Example1.<init>(Example1.java:10)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at java.lang.Class.newInstanceImpl(Native Method)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at java.lang.Class.newInstance(Class.java:1130)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
03-12 17:21:55.112: E/AndroidRuntime(2031):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
03-12 17:21:55.112: E/AndroidRuntime(2031):     ... 11 more
03-12 17:22:02.132: E/AndroidRuntime(2050): FATAL EXCEPTION: main
03-12 17:22:02.132: E/AndroidRuntime(2050): java.lang.RuntimeException: Unable to     instantiate activity ComponentInfo{com.example.test/com.example.test.Example1}:  java.lang.NullPointerException
03-12 17:22:02.132: E/AndroidRuntime(2050):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at  android.os.Handler.dispatchMessage(Handler.java:99)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at android.os.Looper.loop(Looper.java:137)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at android.app.ActivityThread.main(ActivityThread.java:5103)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at java.lang.reflect.Method.invokeNative(Native Method)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at java.lang.reflect.Method.invoke(Method.java:525)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at dalvik.system.NativeStart.main(Native Method)
03-12 17:22:02.132: E/AndroidRuntime(2050): Caused by: java.lang.NullPointerException
03-12 17:22:02.132: E/AndroidRuntime(2050):     at  android.app.Activity.findViewById(Activity.java:1853)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at com.example.test.Example1.<init>(Example1.java:10)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at java.lang.Class.newInstanceImpl(Native Method)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at java.lang.Class.newInstance(Class.java:1130)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
03-12 17:22:02.132: E/AndroidRuntime(2050):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128)
03-12 17:22:02.132: E/AndroidRuntime(2050):     ... 11 more

1 个答案:

答案 0 :(得分：0)

您正在从Activity构造函数中调用findViewById。您无法通过调用findViewById设置活动视图后调用setContentView，这应该在onCreate中完成。例如：

class MyActivity extends Activity {
    public MyActivity() {
        // Do not do anything with views here
    }

    public void onCreate(final Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.myLayout);
        // Now you can do stuff with your views
        final TextView title_view = (TextView)findViewById(R.id.titleView);
    }
}
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