[英]Cannot launch DialogPreference programmatically (Null Pointer Exception thrown)
我有一個擴展DialogPreference的自定義類。 如果從“首選項”菜單啟動,它將完美運行。 我希望能夠從Activity中啟動它。 下面是我的DialogPreference類,其中我公開了此線程建議的showDialog()方法。 當我調用它時,我得到一個空指針異常,但無法找出原因。
在第27行拋出錯誤,它位於onBindDialogView()中,其中調用了hText.setText()。
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“測試”按鈕嘗試從另一個Activity啟動對話框:
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;
}
}
以下是我的首選項和對話首選項的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}
誰知道我做錯了什么? 謝謝!
最好的答案可以在這里找到,但我認為它只需要一點澄清,因為答案錯誤地暗示了清單的兩種不同的樣式聲明。
如果要從Activity啟動一個對話框並仍然能夠從Preference啟動它,您只需創建一個啟動Dialog的Activity。 然后,可以在Preference XML中或另一個Activity中啟動該Activity。 訣竅在於你如何設計風格。 您希望將“活動”設置為對話框的樣式。 這樣,您的Activity啟動的對話框看起來是正確的。 這種方法的副作用是在Dialog后面的屏幕中間顯示一個浮動的Action Bar。 解決方法是使用沒有ActionBar的Dialog樣式。 我正在使用Holo.Light主題,所以我把它放在我的AndroidManifest中
<activity android:name=".DemoDialogActivity"
android:theme="@android:style/Theme.Holo.Light.Dialog.NoActionBar" />
拼圖的另一部分是確保你調用finish(); 當你完成時(這是我在OnClickListener中為我的兩個按鈕做的最后一件事)。 如果不這樣做,對話框將關閉,但活動仍將打開,在黑暗的屏幕中間留下一個小的空白矩形。
這是活動的一個工作示例:
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();
}
}
以編程方式啟動它:
Intent launch_dialog = new Intent(getApplicationContext(),
DemoDialogActivity.class);
startActivity(launch_dialog);
或者作為XML中的首選項:
<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>
我已經有一段時間了。 我發現有一種解決方法完全不優雅。 我可以通過在Activity中進行更改來使用xml布局來構建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可以從這樣的按鈕啟動(case語句來自作為原始問題的一部分粘貼的代碼):
case R.id.testing:
FragmentManager fm = getFragmentManager();
HCDialog hack_dialog = new HCDialog();
hack_dialog.show(fm, null);
return true;
這有效。 但對我來說,這似乎相當愚蠢,我想我已經走了很長一段路。 特別是因為現在我將編碼來處理兩個版本的持久偏好值,這兩個版本似乎是完全相同的對話框。
有沒有更好的辦法?
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