java - 单击时显示对话框首选项

Question

我有一个 PreferenceActivity，其中有一个偏好。我想单击此首选项将打开另一个类中存在的对话框。 Brightness 类包含要渲染的对话框。这是代码。

// This is the PreferenceActivity Class (Settings)
Preference bright;
bright = (Preference) this.findPreference("bri");
bright.setOnPreferenceClickListener( new OnPreferenceClickListener() {
            public boolean onPreferenceClick(Preference preference) {

                Brightness brightness = new Brightness();
                brightness.ShowDialog();

                return true;

            }
            });

亮度等级

public class Brightness extends Activity{

    private SeekBar brightbar;
    private int brightness;
    @SuppressWarnings("unused")
    private ContentResolver cResolver;
    private Window window;
    TextView txtPerc;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        ShowDialog();

    }


    public void ShowDialog() {
    final AlertDialog.Builder popDialog = new AlertDialog.Builder(getApplicationContext());
    final LayoutInflater inflater = (LayoutInflater) this.getSystemService(LAYOUT_INFLATER_SERVICE);
    final View Viewlayout = inflater.inflate(R.layout.dialog_brightness, (ViewGroup) findViewById(R.id.layout_dialog));  

        popDialog.setTitle("Set Brightness");
        popDialog.setView(Viewlayout);

    brightbar = (SeekBar) findViewById(R.id.brightbar);
    txtPerc = (TextView) findViewById(R.id.txtPercentage);
    cResolver = getContentResolver();
    window = getWindow();
    brightbar.setMax(255);
    brightbar.setKeyProgressIncrement(1);

    brightbar = (SeekBar) findViewById(R.id.brightbar);
    txtPerc = (TextView) findViewById(R.id.txtPercentage);
    cResolver = getContentResolver();
    window = getWindow();
    brightbar.setMax(255);
    brightbar.setKeyProgressIncrement(1);

    try
    {
        brightness = Settings.System.getInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS);
        float perc = (brightness /(float)255)*100;
        txtPerc.setText((int)perc +" %");
    }
    catch (SettingNotFoundException e)
    {
        Log.e("Error", "Cannot access system brightness");
        e.printStackTrace();
    }

    brightbar.setProgress(brightness);
    brightbar.setOnSeekBarChangeListener(new OnSeekBarChangeListener()
    {
        public void onStopTrackingTouch(SeekBar seekBar)
        {
            Settings.System.putInt(getContentResolver(), Settings.System.SCREEN_BRIGHTNESS, brightness);
            LayoutParams layoutpars = window.getAttributes();
            layoutpars.screenBrightness = brightness / (float)255;
            window.setAttributes(layoutpars);
        }

        public void onStartTrackingTouch(SeekBar seekBar)
        {

        }

        public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser)
        {


                brightness = progress;

                float perc = (brightness /(float)255)*100;
                txtPerc.setText((int)perc +" %");
        }
    });     

    popDialog.setNeutralButton("Close",
            new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    dialog.dismiss();
                }

            });

    popDialog.create();
    popDialog.show();

}
}

问题是，当我单击此首选项时，应用程序崩溃了!这是日志猫

11-11 18:03:57.788: E/AndroidRuntime(18672): FATAL EXCEPTION: main 11-11 18:03:57.788: E/AndroidRuntime(18672): java.lang.NullPointerException 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:109) 11-11 18:03:57.788: E/AndroidRuntime(18672): at com.packagename.Brightness.ShowDialog(Brightness.java:39) 11-11 18:03:57.788: E/AndroidRuntime(18672): at com.packagename.Settings$1.onPreferenceClick(Settings.java:48) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.preference.Preference.performClick(Preference.java:952) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.preference.PreferenceScreen.onItemClick(PreferenceScreen.java:215) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.widget.AdapterView.performItemClick(AdapterView.java:297) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.widget.AbsListView.performItemClick(AbsListView.java:1100) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.widget.AbsListView$PerformClick.run(AbsListView.java:2788) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.widget.AbsListView$1.run(AbsListView.java:3463) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.os.Handler.handleCallback(Handler.java:730) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.os.Handler.dispatchMessage(Handler.java:92) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.os.Looper.loop(Looper.java:137) 11-11 18:03:57.788: E/AndroidRuntime(18672): at android.app.ActivityThread.main(ActivityThread.java:5289) 11-11 18:03:57.788: E/AndroidRuntime(18672): at java.lang.reflect.Method.invokeNative(Native Method) 11-11 18:03:57.788: E/AndroidRuntime(18672): at java.lang.reflect.Method.invoke(Method.java:525) 11-11 18:03:57.788: E/AndroidRuntime(18672): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739) 11-11 18:03:57.788: E/AndroidRuntime(18672): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555) 11-11 18:03:57.788: E/AndroidRuntime(18672): at dalvik.system.NativeStart.main(Native Method)

Answer 1

要显示对话框，您必须从 Dialog 或 Fragment 而不是 Activity 扩展 Brightness。