我正在创建一个应用程序，现在应该保存，然后获取数字编辑文本的值。当我从string.xml加载数据时，它很好，但当我切换到SharedPreferences时，它甚至没有开始。任何帮助找到问题将不胜感激。 BTW .java在下面，我确定布局.xml没问题。
package programmingandroidapps.brightnesscustomizationapp;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;
import android.util.Log;
import android.content.SharedPreferences;
import android.content.Context;
public class MainActivity extends AppCompatActivity {
//Declarations
String brightnessValue;
int choice, brightnessValueInt;
final EditText mEditText1=(EditText)findViewById(R.id.editText1), mEditText2=(EditText)findViewById(R.id.editText2), mEditText3=(EditText)findViewById(R.id.editText3), mEditText4=(EditText)findViewById(R.id.editText4), mEditText5=(EditText)findViewById(R.id.editText5);
Button mButton1=(Button)findViewById(R.id.button1), mButton2=(Button)findViewById(R.id.button2), mButton3=(Button)findViewById(R.id.button3), mButton4=(Button)findViewById(R.id.button4), mButton5=(Button)findViewById(R.id.button5);
SharedPreferences storedBrightness1 = this.getSharedPreferences("brightv1", Context.MODE_PRIVATE), storedBrightness2 = this.getSharedPreferences("brightv2", Context.MODE_PRIVATE), storedBrightness3 = this.getSharedPreferences("brightv3", Context.MODE_PRIVATE), storedBrightness4 = this.getSharedPreferences("brightv4", Context.MODE_PRIVATE), storedBrightness5 = this.getSharedPreferences("brightv5", Context.MODE_PRIVATE);
SharedPreferences.Editor mEditor;
//
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Get saved brightness values from string.xml and set them to ediText1-5
brightnessValueInt = storedBrightness1.getInt("brightv1", 0);
brightnessIntToString();
printToEditText(1);
brightnessValueInt = storedBrightness2.getInt("brightv2", 0);
brightnessIntToString();
printToEditText(2);
brightnessValueInt = storedBrightness3.getInt("brightv3", 0);
brightnessIntToString();
printToEditText(3);
brightnessValueInt = storedBrightness4.getInt("brightv4", 0);
brightnessIntToString();
printToEditText(4);
brightnessValueInt = storedBrightness5.getInt("brightv5", 0);
brightnessIntToString();
printToEditText(5);
//
// On Click Button Listeners
mButton1.setOnClickListener(
new View.OnClickListener()
{
public void onClick(View view)
{
//Validate >=0 and <=100, paint #222222 if is valid, paint red if not
Log.v(brightnessValue, mEditText1.getText().toString());
mEditor = storedBrightness1.edit();
mEditor.putInt("brightv1", brightnessValueInt);
}
});
//
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void printToEditText(int choice)
{
if(choice==1)
{
mEditText1.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==2)
{
mEditText2.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==3)
{
mEditText3.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==4)
{
mEditText4.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else
{
mEditText5.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
}
public void brightnessIntToString()
{
brightnessValue=brightnessValueInt+"";
}
}
我相信这是应用程序崩溃日志。我是Android的新手，所以如果它不仅仅是说出来，就不必生气了：P
05-01 13:24:53.061 1624-1624/programmingandroidapps.brightnesscustomizationapp D/dalvikvm: Not late-enabling CheckJNI (already on)
05-01 13:24:56.451 1624-1624/programmingandroidapps.brightnesscustomizationapp D/AndroidRuntime: Shutting down VM
05-01 13:24:56.451 1624-1624/programmingandroidapps.brightnesscustomizationapp W/dalvikvm: threadid=1: thread exiting with uncaught exception (group=0xb3d11b20)
05-01 13:24:56.471 1624-1624/programmingandroidapps.brightnesscustomizationapp E/AndroidRuntime:
FATAL EXCEPTION: main
Process: programmingandroidapps.brightnesscustomizationapp, PID: 1624
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{programmingandroidapps.brightnesscustomizationapp/programmingandroidapps.brightnesscustomizationapp.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.app.Activity.findViewById(Activity.java:1884)
at programmingandroidapps.brightnesscustomizationapp.MainActivity.<init>(MainActivity.java:21)
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1208)
at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2101)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：2)
问题是，在应用布局并初始化活动（findViewById）之前，您正在调用getSharedPreferences和this。您应该在onCreate之后将这些方法调用放在setContentView(R.layout.activity_main);。
答案 1 :(得分：1)
Dejan将部分代码移入onCreate生命周期方法是正确的，具体来说，您的代码应该更改为：
package programmingandroidapps.brightnesscustomizationapp;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Button;
import android.util.Log;
import android.content.SharedPreferences;
import android.content.Context;
public class MainActivity extends AppCompatActivity {
//Declarations
String brightnessValue;
int choice, brightnessValueInt;
private EditText mEditText1, mEditText2, mEditText3, mEditText4, mEditText5;
private Button mButton1,mButton2, mButton3, mButton4, mButton5;
private SharedPreferences storedBrightness1, storedBrightness2, storedBrightness3,storedBrightness4,storedBrightness5;
private SharedPreferences.Editor mEditor;
//
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mButton1 =(Button)findViewById(R.id.button1);
mButton2=(Button)findViewById(R.id.button2);
mButton3=(Button)findViewById(R.id.button3);
mButton4=(Button)findViewById(R.id.button4);
mButton5=(Button)findViewById(R.id.button5);
mEditText1 =(EditText)findViewById(R.id.editText1);
mEditText2=(EditText)findViewById(R.id.editText2);
mEditText3=(EditText)findViewById(R.id.editText3);
mEditText4=(EditText)findViewById(R.id.editText4);
mEditText5=(EditText)findViewById(R.id.editText5);
//instead of doing this, I'd rather use "named" SharedPreferences - call it "brightness" and will carry the five values
//something like SharedPreferences brightnessPreferences = this.getSharedPreferences("brightness", Context.MODE_PRIVATE);
//I ma just adding this here because that's the way you have it
storedBrightness1 = this.getSharedPreferences("brightv1", Context.MODE_PRIVATE),
storedBrightness2 = this.getSharedPreferences("brightv2", Context.MODE_PRIVATE),
storedBrightness3 = this.getSharedPreferences("brightv3", Context.MODE_PRIVATE),
storedBrightness4 = this.getSharedPreferences("brightv4", Context.MODE_PRIVATE),
storedBrightness5 = this.getSharedPreferences("brightv5", Context.MODE_PRIVATE);
//Get saved brightness values from string.xml and set them to ediText1-5
brightnessValueInt = storedBrightness1.getInt("brightv1", 0);
brightnessIntToString();
printToEditText(1);
brightnessValueInt = storedBrightness2.getInt("brightv2", 0);
brightnessIntToString();
printToEditText(2);
brightnessValueInt = storedBrightness3.getInt("brightv3", 0);
brightnessIntToString();
printToEditText(3);
brightnessValueInt = storedBrightness4.getInt("brightv4", 0);
brightnessIntToString();
printToEditText(4);
brightnessValueInt = storedBrightness5.getInt("brightv5", 0);
brightnessIntToString();
printToEditText(5);
//
// On Click Button Listeners
mButton1.setOnClickListener(
new View.OnClickListener()
{
public void onClick(View view)
{
//Validate >=0 and <=100, paint #222222 if is valid, paint red if not
Log.v(brightnessValue, mEditText1.getText().toString());
mEditor = storedBrightness1.edit();
mEditor.putInt("brightv1", brightnessValueInt);
}
});
//
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void printToEditText(int choice)
{
if(choice==1)
{
mEditText1.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==2)
{
mEditText2.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==3)
{
mEditText3.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else if(choice==4)
{
mEditText4.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
else
{
mEditText5.setText(brightnessValue, TextView.BufferType.EDITABLE);
}
}
public void brightnessIntToString()
{
brightnessValue=brightnessValueInt+"";
}
}