Question

我只是android编程的初学者，目前我正在android中创建一个简单的项目。但是我面临很多错误。我几乎没有疑问：

1）每当我创建一个项目时，它创建一个两个布局 activity_main.xml和fragment_main.xml 我知道什么是片段但我很困惑哪一个使用......！有人说只需使用 fragment_main.xml 来设计所有活动。这是对的吗？或者我还需要使用 activity_main ？

2）我创建了一个应用程序，它首先显示闪存屏幕，然后进入活动但是当我运行应用程序时，它显示不幸的是应用程序停止了，代码是

SplashActivity：

public class SplashActivity extends Activity {

private static int SPLASH_TIME_OUT = 3000;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fragment_splash);

    new Handler().postDelayed(new Runnable() {

        @Override
        public void run() {
            // This method will be executed once the timer is over
            // Start your app main activity
            Intent i = new Intent(SplashActivity.this, AboutUs.class);
            startActivity(i);

            // close this activity
            finish();
        }
    }, SPLASH_TIME_OUT);
}}

关于我们：

public class AboutUs extends Activity implements OnClickListener {

TextView tv_au1;
TextView tv_woff;
Button btn_go;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_about_us);

    tv_au1=(TextView) findViewById(R.id.textView1);
    tv_woff=(TextView) findViewById(R.id.textView2);
    btn_go=(Button) findViewById(R.id.button1);
    btn_go.setOnClickListener(this);

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

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.about_us, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {

    public PlaceholderFragment() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_about_us,
                container, false);
        return rootView;
    }
}

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub
    Intent go_create_note = new Intent(this, Dashboard.class);
    startActivity(go_create_note);

}}

我的项目中没有任何错误，我的logcat是：

05-08 13:00:05.790: E/AndroidRuntime(847):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.app.ActivityThread.access$800(ActivityThread.java:135)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.os.Handler.dispatchMessage(Handler.java:102)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.os.Looper.loop(Looper.java:136)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.app.ActivityThread.main(ActivityThread.java:5017)
05-08 13:00:05.790: E/AndroidRuntime(847):  at java.lang.reflect.Method.invokeNative(Native Method)
05-08 13:00:05.790: E/AndroidRuntime(847):  at java.lang.reflect.Method.invoke(Method.java:515)
05-08 13:00:05.790: E/AndroidRuntime(847):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-08 13:00:05.790: E/AndroidRuntime(847):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-08 13:00:05.790: E/AndroidRuntime(847):  at dalvik.system.NativeStart.main(Native Method)
05-08 13:00:05.790: E/AndroidRuntime(847): Caused by: java.lang.NullPointerException
05-08 13:00:05.790: E/AndroidRuntime(847):  at com.example.notedip.AboutUs.onCreate(AboutUs.java:32)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.app.Activity.performCreate(Activity.java:5231)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-08 13:00:05.790: E/AndroidRuntime(847):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
05-08 13:00:05.790: E/AndroidRuntime(847):  ... 11 more

任何人都能解释一下吗？非常感谢提前

Answer 1

我猜视图属于fragment_about_us.xml，在这种情况下你需要在Fragment中初始化视图

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_about_us,
            container, false);
    tv_au1=(TextView) rootView.findViewById(R.id.textView1);
    tv_woff=(TextView) rootView.findViewById(R.id.textView2);
    btn_go=(Button) rootView.findViewById(R.id.button1);
    btn_go.setOnClickListener(this);

    return rootView;
}

更改此

public static class PlaceholderFragment extends Fragment {

到

public static class PlaceholderFragment extends Fragment implements OnClickListener{

然后将下面的内容移到片段类

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent go_create_note = new Intent(getActivity(), Dashboard.class);
startActivity(go_create_note);

}

不幸的是Android应用已停止：但在项目中没有发现错误

1 个答案: