Question

当我点击操作栏中的操作项时，我正在尝试调用一个新的Activity（“OtherActivity”）但是它给了我java.lang.RuntimeException：无法启动活动ComponentInfo。

我在manifest.xml文件中指定了MainActivity和OtherActivity。

package com.example.notice;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button btn = (Button)findViewById(R.id.action_settings);
    btn.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            Intent i = new               Intent(MainActivity.this,OtherActivity.class);
            startActivity(i);
        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

}

这是我的LogCat

12-08 01:51:38.118: E/AndroidRuntime(2823): FATAL EXCEPTION: main
12-08 01:51:38.118: E/AndroidRuntime(2823): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.notice/com.example.notice.MainActivity}: java.lang.NullPointerException
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.os.Looper.loop(Looper.java:137)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.app.ActivityThread.main(ActivityThread.java:5103)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at java.lang.reflect.Method.invokeNative(Native Method)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at java.lang.reflect.Method.invoke(Method.java:525)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at dalvik.system.NativeStart.main(Native Method)
12-08 01:51:38.118: E/AndroidRuntime(2823): Caused by: java.lang.NullPointerException
12-08 01:51:38.118: E/AndroidRuntime(2823):     at com.example.notice.MainActivity.onCreate(MainActivity.java:17)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.app.Activity.performCreate(Activity.java:5133)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-08 01:51:38.118: E/AndroidRuntime(2823):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
12-08 01:51:38.118: E/AndroidRuntime(2823):     ... 11 more

OtherActivity

package com.example.notice;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class OtherActivity extends Activity {

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

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.other, menu);
    return true;
}

}

Answer 1

问题是Button activity_main.xml中id没有action_settings。因此，当您尝试在其上设置NPE时，您会获得OnClickListener。如果是menu，那么您需要使用onOptionsItemSelected()。

我们知道这一点，因为在这里看这两行

Caused by: java.lang.NullPointerException
12-08 01:51:38.118: E/AndroidRuntime(2823):     at     
com.example.notice.MainActivity.onCreate(MainActivity.java:17)

它表示null的第17行MainActivity处有listener，这是您设置{{1}}的地方，意味着它没有被正确化。

OnOptionsItemSelected Docs

Answer 2

最有可能是这一行

Button btn = (Button)findViewById(R.id.action_settings);

是一个麻烦制造者：确保你正确地启动你的btn - 看起来像是空的

Answer 3

action_setting是一个菜单项，而不是活动布局中的Button，因此您应该使用按钮名称（在活动布局'R.layout.activity_main'中）。不是菜单项

如何调试“java.lang.RuntimeException：无法启动活动ComponentInfo”？

3 个答案: