无法启动活动，setOnClickListener

Question

无法开始新活动。 onClickListener 出现问题。

我发布了一个错误代码。不知道为什么我在这一行出错。

我觉得可以不初始化变量Button b，但是已经初始化了！

请帮忙

代码：

public class newItem extends Activity {
    private EditText Quantity;
    private EditText Weight;
    private EditText Price;
    private EditText Title;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.new_list);
        this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);

        Button b = (Button) findViewById(R.id.ok_but);
        Quantity = (EditText) findViewById(R.id.Quantity);
        Weight = (EditText) findViewById(R.id.Weight);
        Price = (EditText) findViewById(R.id.Price);
        Title = (EditText) findViewById(R.id.Title);

        b.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent i = new Intent();
                i.putExtra("Quantity", Quantity.getText().toString());
                i.putExtra("Weight", Weight.getText().toString());
                i.putExtra("Price", Price.getText().toString());
                i.putExtra("Title", Title.getText().toString());
                setResult(RESULT_OK, i);
                Log.i("palval", "setResult(RESULT_OK, i); newItem");
                finish();
            }
        });
    }
}

错误：

07-08 17:26:42.402: E/AndroidRuntime(31626): FATAL EXCEPTION: main
07-08 17:26:42.402: E/AndroidRuntime(31626): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ashopping_list/com.example.ashopping_list.newItem}: java.lang.NullPointerException
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2194)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2229)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.app.ActivityThread.access$600(ActivityThread.java:139)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.os.Looper.loop(Looper.java:154)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.app.ActivityThread.main(ActivityThread.java:4945)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at java.lang.reflect.Method.invokeNative(Native Method)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at java.lang.reflect.Method.invoke(Method.java:511)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at dalvik.system.NativeStart.main(Native Method)
07-08 17:26:42.402: E/AndroidRuntime(31626): Caused by: java.lang.NullPointerException
07-08 17:26:42.402: E/AndroidRuntime(31626):    at com.example.ashopping_list.newItem.onCreate(newItem.java:32)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.app.Activity.performCreate(Activity.java:4531)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1071)
07-08 17:26:42.402: E/AndroidRuntime(31626):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2150)

清单：

    <activity
        android:name=".newItem"
        android:label="@string/title_activity_main"
        android:windowSoftInputMode="stateAlwaysVisible" >
    </activity>

这里出错了：

b.setOnClickListener(new OnClickListener() {

Answer 1

尝试使用

implements View.OnClickListener

或者尝试使用 Listener 作为匿名类，然后告诉我它是否有效。

注意：类名应该以大写开头，你应该尊重它。

更新：

所以问题出在其他地方，请确保您的 ID 是正确的！属于Button。

Answer 2

你可以这样试试：

     Button b= (Button) findViewById(R.id.but_Ok);
     b.setOnClickListener(new OnClickListener() {
        public void onClick(View v)
             {
                     Intent i = new Intent(FromYourActivity.this,NextActivity.class);
                     startActivity(i);
                     finish();
                    ...
             }
       });

还要确保您的 XML 文件中有正确的 Button 定义

     <Button 
     android:layout_height="wrap_content"
     android:id="@+id/but_Ok" 
     android:text="Your Button Text"
     android:layout_width="fill_parent"
     />

Answer 3

你需要在onCreate(Bundle)上面设置按钮变量我也改变了onclick活动的设置方式试试这个

public class newItem extends Activity {

private EditText Quantity;
Button b;

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

    public void onClick(View v) {
    // TODO Auto-generated method stub
    Intent i = new Intent();
    ...
    setResult(RESULT_OK, i);
    finish();
    }
});


    }
}