java - 无法以编程方式启动 DialogPreference（抛出空指针异常）

Question

我有一个扩展 DialogPreference 的自定义类。如果从“首选项”菜单启动，它会完美运行。我也希望能够从 Activity 启动它。下面是我的 DialogPreference 类，我在其中公开了这个线程建议的 showDialog() 方法。当我调用它时，我得到一个空指针异常，但无法弄清楚原因。

在调用 hText.setText() 的 onBindDialogView() 中的第 27 行引发错误。

package com.jumptuck.recipebrowser;

import android.content.Context;
import android.content.SharedPreferences;
import android.preference.DialogPreference;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.widget.EditText;

// Pop-up dialog used to set and modify host and login credentials
public class HostCredentialsDialogPreference extends DialogPreference {
    static final String TAG = "HostCredentialsDialogPreference";
    EditText hText, uText, pText;

    public HostCredentialsDialogPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
        setDialogLayoutResource(R.layout.dialog_host_credentials);
    }

    @Override
    protected void onBindDialogView(View view) {
        super.onBindDialogView(view);
        Log.d(TAG,"onBindDialogView");

        SharedPreferences sp = getSharedPreferences();
        hText.setText(sp.getString("host", ""));
        uText.setText(sp.getString("username", ""));
        pText.setText(sp.getString("password", ""));
    }

    @Override
    protected View onCreateDialogView() {
        // Guide for this technique found at:
        // http://alexfu.tumblr.com/post/23683149440/android-dev-custom-dialogpreference
        Log.d(TAG,"onCreateDialogView");
        View root = super.onCreateDialogView();
        hText = (EditText) root.findViewById(R.id.host);
        uText = (EditText) root.findViewById(R.id.username);
        pText = (EditText) root.findViewById(R.id.password);
        return root;
    }

    @Override
    protected void onDialogClosed(boolean positiveResult) {
        super.onDialogClosed(positiveResult);
        if (positiveResult){
            Log.d(TAG,"Clicked Save");
            SharedPreferences sp = getSharedPreferences();
            SharedPreferences.Editor editor = sp.edit();
            editor.putString("host", hText.getText().toString());
            editor.putString("username", uText.getText().toString());
            editor.putString("password", pText.getText().toString());
            editor.commit();
        }
        else {
            Log.d(TAG,"Clicked Cancel");
        }
    }

    void show() {
        showDialog(null);
    }

}

我正在使用“测试”按钮尝试从另一个活动启动对话框：

public boolean onOptionsItemSelected(MenuItem item) {
    Log.d(TAG, "onOptionsItemSelected");

    switch (item.getItemId()) {
    case R.id.item_prefs:
        startActivity(new Intent(this, PrefsActivity.class));
        return true;
    case R.id.refresh:
        if (credentialsExist()) {
            refreshListView();
        }
        return true;
    case R.id.recipe_dir:
        startActivity(new Intent(this, RecipeDisplayActivity.class));
        return true;
    case R.id.testing:
        HostCredentialsDialogPreference hc = new HostCredentialsDialogPreference(this, null);
        hc.show();
        return true;

    default:
        return false;
    }
}

以下是我的首选项和对话框首选项的 xml 文件：

<?xml version="1.0" encoding="utf-8"?>

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >
    <com.jumptuck.recipebrowser.HostCredentialsDialogPreference
        android:key="dialog_credentials"
        android:title="Server Address and Login"
        android:summary="Set Host, Username and Password" />

</PreferenceScreen>

和

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/dialog_hostname_label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/dialog_hint_uri" />

    <EditText
        android:id="@+id/host"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="textUri" />

    <TextView
        android:id="@+id/dialog_username_label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/dialog_hint_user" />

    <EditText
        android:id="@+id/username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="text" />

    <TextView
        android:id="@+id/dialog_password_label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/dialog_hint_password" />

    <EditText
        android:id="@+id/password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:fontFamily="sans-serif"
        android:inputType="textPassword" />

</LinearLayout>

最后是 Logcat：

D/RecipeListActivity( 5894): onOptionsItemSelected
D/HostCredentialsDialogPreference( 5894): onCreateDialogView
D/HostCredentialsDialogPreference( 5894): onBindDialogView
D/AndroidRuntime( 5894): Shutting down VM
W/dalvikvm( 5894): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
E/AndroidRuntime( 5894): FATAL EXCEPTION: main
E/AndroidRuntime( 5894): java.lang.NullPointerException
E/AndroidRuntime( 5894):    at com.jumptuck.recipebrowser.HostCredentialsDialogPreference.onBindDialogView(HostCredentialsDialogPreference.java:27)
E/AndroidRuntime( 5894):    at android.preference.DialogPreference.showDialog(DialogPreference.java:289)
E/AndroidRuntime( 5894):    at com.jumptuck.recipebrowser.HostCredentialsDialogPreference.show(HostCredentialsDialogPreference.java:62)
E/AndroidRuntime( 5894):    at com.jumptuck.recipebrowser.RecipeListActivity.onOptionsItemSelected(RecipeListActivity.java:192)
E/AndroidRuntime( 5894):    at android.app.Activity.onMenuItemSelected(Activity.java:2534)
E/AndroidRuntime( 5894):    at com.android.internal.policy.impl.PhoneWindow.onMenuItemSelected(PhoneWindow.java:958)
E/AndroidRuntime( 5894):    at com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:735)
E/AndroidRuntime( 5894):    at com.android.internal.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:149)
E/AndroidRuntime( 5894):    at com.android.internal.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:874)
E/AndroidRuntime( 5894):    at com.android.internal.view.menu.ListMenuPresenter.onItemClick(ListMenuPresenter.java:166)
E/AndroidRuntime( 5894):    at android.widget.AdapterView.performItemClick(AdapterView.java:298)
E/AndroidRuntime( 5894):    at android.widget.AbsListView.performItemClick(AbsListView.java:1086)
E/AndroidRuntime( 5894):    at android.widget.AbsListView$PerformClick.run(AbsListView.java:2859)
E/AndroidRuntime( 5894):    at android.widget.AbsListView$1.run(AbsListView.java:3533)
E/AndroidRuntime( 5894):    at android.os.Handler.handleCallback(Handler.java:615)
E/AndroidRuntime( 5894):    at android.os.Handler.dispatchMessage(Handler.java:92)
E/AndroidRuntime( 5894):    at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime( 5894):    at android.app.ActivityThread.main(ActivityThread.java:4745)
E/AndroidRuntime( 5894):    at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime( 5894):    at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime( 5894):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
E/AndroidRuntime( 5894):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
E/AndroidRuntime( 5894):    at dalvik.system.NativeStart.main(Native Method)
W/ActivityManager(  148):   Force finishing activity com.jumptuck.recipebrowser/.RecipeListActivity
W/WindowManager(  148): Failure taking screenshot for (246x410) to layer 21025
W/ActivityManager(  148): Activity pause timeout for ActivityRecord{412097e0 com.jumptuck.recipebrowser/.RecipeListActivity}
I/Choreographer(  281): Skipped 39 frames!  The application may be doing too much work on its main thread.
W/ActivityManager(  148): Activity destroy timeout for ActivityRecord{412097e0 com.jumptuck.recipebrowser/.RecipeListActivity}

有人知道我在做什么错吗？谢谢！

Answer 1

最好的答案可以在这里找到，但我认为它只需要一点澄清，因为该答案错误地暗示了清单的两种不同样式声明。

如果您想从 Activity 启动一个对话框并且仍然能够从 Preference 中启动它，您只需要创建一个启动 Dialog 的 Activity。然后，该 Activity 可以作为 Preference XML 中的意图或从另一个 Activity 启动。诀窍在于你如何设计它。您想将 Activity 设置为对话框。这样，您的 Activity 启动的对话框将看起来正确。这种方法的副作用是在 Dialog 后面的屏幕中间会显示一个浮动的 Action Bar。解决方法是使用没有 ActionBar 的 Dialog 样式。我正在使用 Holo.Light 主题所以我把它放在我的 AndroidManifest

<activity android:name=".DemoDialogActivity"
            android:theme="@android:style/Theme.Holo.Light.Dialog.NoActionBar" />

难题的另一部分是确保您调用了 finish(); 当你完成时（这是我在 OnClickListener 中为我的两个按钮所做的最后一件事）。如果不这样做，对话框将关闭，但 Activity 仍将打开，在变暗的屏幕中间留下一个小的空白矩形。

这是 Activity 的一个工作示例：

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;

public class DemoDialogActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        LayoutInflater lf = LayoutInflater.from(this);
        // This adds XML elements as a custom view (optional):
        final View customElementsView = lf.inflate(
                R.layout.activity_credentials, null);
        AlertDialog alert = new AlertDialog.Builder(this)
                // This adds the custom view to the Dialog (optional):
                .setView(customElementsView)
                .setTitle("This is the Title")
                .setMessage("This is the AlertDialog message (optional)")
                .setNegativeButton("Cancel",
                        new DialogInterface.OnClickListener() {

                            @Override
                            public void onClick(DialogInterface dialog,
                                    int which) {
                                // Cancel was clicked; do something
                                // Close Activity
                                finish();
                            }
                        })
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {

                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        // OK was clicked; do something
                        // Close Activity
                        finish();
                    }
                }).create();

        // Show the dialog
        alert.show();
    }
}

以编程方式启动它：

Intent launch_dialog = new Intent(getApplicationContext(),
    DemoDialogActivity.class);
startActivity(launch_dialog);

或作为 XML 中的首选项：

<Preference
    android:key="demo_dialog"
    android:title="Title of item on Prefs screen"
    android:summary="This will be small text below the title">
    <intent
        android:action="android.intent.action.VIEW"
        android:targetClass="com.example.package.DemoDialogActivity"
        android:targetPackage="com.example.package" />
</Preference>

Answer 2

我已经为此工作了一段时间。有一种解决方法我觉得完全不优雅。我可以通过在 Activity 中进行更改来使用 xml 布局来构建 DialogFragment：

class HCDialog extends DialogFragment {

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        LayoutInflater inflater = getActivity().getLayoutInflater();
        View view = inflater.inflate(R.layout.dialog_host_credentials, null);
        builder.setView(view);
        builder.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub

            }
        })
        .setNegativeButton(android.R.string.cancel, new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                // TODO Auto-generated method stub

            }
        });
        builder.setTitle(R.string.dialog_title);
        return builder.create();
    }
}

DialogFragment 可以从这样的按钮启动（案例语句来自作为我原始问题的一部分粘贴的代码）：

    case R.id.testing:
        FragmentManager fm = getFragmentManager();
        HCDialog hack_dialog = new HCDialog();
        hack_dialog.show(fm, null);
        return true;

这行得通。但对我来说，这似乎很愚蠢，我想我正在走很长的路。特别是因为现在我将编写代码来处理看似完全相同的对话框的两个版本的持久偏好值。

有没有更好的办法？