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嗨，我是 android 编程的初学者，我正在使用数据库。我正在关注一个视频，当我尝试运行该应用程序时，我不断收到此消息“应用程序已意外停止。请重试”我不知道我做错了什么。谢谢

08-14 20:43:08.950: E/AndroidRuntime(378): FATAL EXCEPTION: main
08-14 20:43:08.950: E/AndroidRuntime(378): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.seenit/com.example.seenit.MainActivity}: java.lang.NullPointerException
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.os.Handler.dispatchMessage(Handler.java:99)
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.os.Looper.loop(Looper.java:123)
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.app.ActivityThread.main(ActivityThread.java:3683)
08-14 20:43:08.950: E/AndroidRuntime(378):  at java.lang.reflect.Method.invokeNative(Native Method)
08-14 20:43:08.950: E/AndroidRuntime(378):  at java.lang.reflect.Method.invoke(Method.java:507)
08-14 20:43:08.950: E/AndroidRuntime(378):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
08-14 20:43:08.950: E/AndroidRuntime(378):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
08-14 20:43:08.950: E/AndroidRuntime(378):  at dalvik.system.NativeStart.main(Native Method)
08-14 20:43:08.950: E/AndroidRuntime(378): Caused by: java.lang.NullPointerException
08-14 20:43:08.950: E/AndroidRuntime(378):  at com.example.seenit.MainActivity.onCreate(MainActivity.java:28)
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-14 20:43:08.950: E/AndroidRuntime(378):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
08-14 20:43:08.950: E/AndroidRuntime(378):  ... 11 more

这是我的 MainActivity.java

import android.app.Activity;
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener {
/** Called when the activity is first created. */
EditText movie, director, actors, genre;
Button bUpdate, bView;

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

    movie = (EditText) findViewById(R.id.etMovie);
    director = (EditText) findViewById(R.id.etDirector);
    actors = (EditText) findViewById(R.id.etActors);
    genre = (EditText) findViewById(R.id.etGenre);

    bUpdate.setOnClickListener(this);
    bView.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub
    switch(v.getId()) {
        case R.id.bUpdate:
            boolean works = true;
            try {
                String mov = movie.getText().toString();
                String dir = director.getText().toString();
                String act = actors.getText().toString();
                String gen = genre.getText().toString();

                SeenIt entry = new SeenIt(MainActivity.this);
                entry.open();
                entry.createEntry(mov, dir, act, gen);
                entry.close();

            }catch(Exception e) {
                works = false;
                String error = e.toString();
                Dialog d = new Dialog(this);
                d.setTitle("@+id/Works");
                TextView tv = new TextView(this);
                tv.setText(error);
                d.setContentView(tv);
                d.show();
            }finally {
                if(works) {

                    Dialog d = new Dialog(this);
                    d.setTitle("@+id/dWorks");
                    TextView tv = new TextView(this);
                    tv.setText("@+id/tvWorks");
                    d.setContentView(tv);
                    d.show();
                }
            }

            break;

        case R.id.bView:
            Intent i = new Intent("com.example.seenit.SQLView");
            startActivity(i);

            break;
    }

}
}
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1 回答 1

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您正在为尚不存在的按钮设置侦听器，这就是您收到 NullerPointerException 的原因。您必须将此代码放在听众之前，就像您对 EditText 所做的那样。

bUpdate = (Button) findViewById(R.id.LayoutNameOfTheButton)
bView = (Button) findViewById(R.id.LayoutNameOfTheButton)

显然，您必须将“LayoutNameOfTheButton”更改为布局中元素的名称。

于 2013-08-14T18:11:36.553 回答