我正在尝试更改主要活动的背景色。我从菜单中选择设置，然后通过设置进入另一个活动。当我单击复选框更改背景时，它崩溃了。我正在尝试更改主要活动视图的背景。 LinearLayout是主要活动的子项，也是我希望更改的子项。但是我一直在获得nullpointer，如何解决该问题或需要什么才能使它起作用呢？
设置活动类：
public class ShowSettingsActivity extends Activity {
static final String TAG = "CAT";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.show_settings_layout);
SharedPreferences sharedPrefs = PreferenceManager.getDefaultSharedPreferences(this);
StringBuilder builder = new StringBuilder();
builder.append("\n" + sharedPrefs.getBoolean("night_mode_key", true));
builder.append("\n" + sharedPrefs.getString("time_usage_key", "-1"));
builder.append("\n" + sharedPrefs.getString("language_key", "-1"));
//builder.append("\n" + sharedPrefs.getBoolean("time_history_key", true));
TextView settingsTextView = (TextView) findViewById(R.id.settings_text_view);
settingsTextView.setText(builder.toString());
}
}
偏好活动类别：
public class QuickPrefsActivity extends PreferenceActivity implements
OnSharedPreferenceChangeListener {
CheckBoxPreference isReg;
static final String TAG = "QuickPrefsActivity";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.preferences);
PreferenceManager.setDefaultValues(this,R.xml.preferences, false);
CheckBoxPreference night_checkbox = (CheckBoxPreference) findPreference("night_mode_key");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
//menu.add(Menu.NONE, 0, 0, "Show current settings");
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case 0:
startActivity(new Intent(this, ShowSettingsActivity.class));
return true;
}
return false;
}
@Override
public void onStart(){
super.onStart();
SharedPreferences prefs=PreferenceManager.getDefaultSharedPreferences(QuickPrefsActivity.this);
}
@Override
protected void onResume() {
super.onResume();
// Set up a listener whenever a key changes
getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
}
@Override
protected void onPause() {
super.onPause();
// Unregister the listener whenever a key changes
getPreferenceScreen().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
}
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
SharedPreferences s = getSharedPreferences("MY_PREFS", 0);
// Create a editor to edit the preferences:
SharedPreferences.Editor editor = s.edit();
// Let's do something a preference value changes
if (key.equals("night_mode_key"))
{
// Create a reference to the checkbox (in this case):
CheckBoxPreference mHints = (CheckBoxPreference)getPreferenceScreen().findPreference("night_mode_key");
//Lets change the summary so the user knows what will happen using a one line IF statement:
//mHints.setSummary(mHints.isChecked() ? "Hints will popup." : "No hints will popup.");
// Lets store the new preference:
//SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
boolean checkBoxValue = s.getBoolean("night_mode_key", false);
if (checkBoxValue)
{
Log.d(TAG, "true onshared" + checkBoxValue);
//setContentView(R.layout.activity_main);
View v = findViewById(R.id.LinearLayout1);
//View root = v.getRootView();
v.setBackgroundColor(0xffffffff);
/*((TextView) findViewById(R.id.hanziTextView)).setTextColor(0xff000000);
((TextView) findViewById(R.id.timerTextView)).setTextColor(0xff000000);
((TextView) findViewById(R.id.instructionTextView)).setTextColor(0xff000000);*/
}
else
{
/* findViewById(R.id.LinearLayout1).setBackgroundColor(0xff000000);
((TextView) findViewById(R.id.hanziTextView)).setTextColor(0xff444444);
((TextView) findViewById(R.id.timerTextView)).setTextColor(0xff444444);
((TextView) findViewById(R.id.instructionTextView)).setTextColor(0xff444444);*/
Log.d(TAG, "false onshared" + checkBoxValue);
}
//checkBox.setChecked(false);
editor.putBoolean("night_mode_key", mHints.isChecked());
// Save the results:
editor.commit();
}
if (key.equals("language_key")) {
sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
//ListPreference listPref = (ListPreference) sharedPreferences;
String entryvalue = sharedPreferences.getString( "language_key", "");
Log.d(TAG, "Entryvalue " + entryvalue);
if (entryvalue.equals("EN"))
{
Log.d(TAG, "EN " + entryvalue);
Toast.makeText(getBaseContext(), "English Selected", Toast.LENGTH_SHORT).show();
}
else if (entryvalue.equals("CH"))
{
Log.d(TAG, "CH " + entryvalue);
Toast.makeText(getBaseContext(), "Chinese Selected", Toast.LENGTH_SHORT).show();
}
else
{
Toast.makeText(getBaseContext(), "You may not go where no1 has gone before, pick again!", Toast.LENGTH_SHORT).show();
}
}
}
}
主布局xml ...我正在尝试更改背景的那个：
<android.support.v4.widget.DrawerLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.gesture.GestureOverlayView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/gestureOverlayView1"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<LinearLayout
android:id="@+id/LinearLayout1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:padding="10dp"
android:layout_gravity="start">
<TextView
android:id="@+id/timerTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="right"
android:layout_marginRight="5sp"
android:text="@string/startTime"
android:textAppearance="?android:attr/textAppearanceSmall"
android:textSize="30sp" />
</LinearLayout>
</android.gesture.GestureOverlayView>
<FrameLayout
android:id="@+id/content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<!-- The navigation drawer -->
<ListView android:id="@+id/left_drawer"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:choiceMode="singleChoice"
android:divider="#666"
android:dividerHeight="1dp"
android:background="#333"
android:paddingLeft="15sp"
android:paddingRight="15sp"
/>
</android.support.v4.widget.DrawerLayout>
它将崩溃，因为目标LinearLayout在另一个活动中。您可以做的是..将背景色或设置的颜色保存在Sharedpreferences文件中。然后在主活动中再次调用它以更改颜色...
if (checkBoxValue)
{
SharedPreferences sp = getSharedPreferences("settings", Context.MODE_PRIVATE);
Editor edit = sp.edit();
edit.putString("COLOR", "0xffffffff")
}
然后在您的主检查中，sharedPreferences的值...
...
SharedPreferences sp = getSharedPreferences("settings", Context.MODE_PRIVATE);
v.setBackgroundColor(sp.getString("COLOR"), Color.WHITE); // here check if the value available, if not put the color to default.. maybe white?...
这是未经测试的代码。我粗略地写了它。但是我希望你能理解。请给我反馈
您无法从另一个活动访问主活动的布局视图。这样做的方法是在意图中添加额外的东西以再次启动主活动，或者可以使用SharedPreferences。