java - 应用程序不断崩溃

Question

我现在已经得到了所有的代码，但总是崩溃。基本上，该代码是一个按钮，单击该按钮会将一个数字添加到一个金额中。所以，点击一次，就是1；再次点击将变成 2，然后是 3，依此类推。

package com.example.counter;

import android.app.Activity;
import android.content.SharedPreferences;
import android.os.Bundle;


public class MainActivity extends Activity {
// Private member field to keep track of the count
private int mCount = 0;

public static final String PREFS_NAME = "com.example.myApp.mCount";
private SharedPreferences settings = null;
private SharedPreferences.Editor editor = null;

/** ADD THIS METHOD **/
@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);  // Always call the superclass method first
  settings = getSharedPreferences(PREFS_NAME, MODE_PRIVATE);
}

@Override
public void onPause() {
  super.onPause();  // Always call the superclass method first
  mCount = settings.getInt("mCount", 0);
}

@Override
public void onResume() {
  super.onResume();  // Always call the superclass method first
  editor = settings.edit(); /** ADD THIS LINE **/
  editor.putInt("mCount", mCount);
  editor.commit();
}
}

xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >

<TextView
    android:id="@+id/TextViewCount"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:text="@string/hello_world" />

<Button
    android:id="@+id/ButtonCount"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_above="@+id/TextViewCount"
    android:layout_alignRight="@+id/TextViewCount"
    android:layout_marginBottom="22dp"
    android:text="Count" />

</RelativeLayout>

Answer 1

您应该在 onCreate() 中创建 SharedPreferences 对象；在此之前，它不能保证被创建。

此外，您应该在每个 onResume() 中调用 edit()；否则，您可能会在该 Editor 中获得旧数据。

public class MainActivity extends Activity {
    // Private member field to keep track of the count
    private int mCount = 0;

    public static final String PREFS_NAME = "com.example.myApp.mCount";
    private SharedPreferences settings = null;
    private SharedPreferences.Editor editor = null;

    /** ADD THIS METHOD **/
    @Override
    public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);  // Always call the superclass method first
      settings = getSharedPreferences(PREFS_NAME, MODE_PRIVATE);
    }

    @Override
    public void onPause() {
      super.onPause();  // Always call the superclass method first
      mCount = settings.getInt("mCount", 0);
    }

    @Override
    public void onResume() {
      super.onResume();  // Always call the superclass method first
      editor = settings.edit(); /** ADD THIS LINE **/
      editor.putInt("mCount", mCount);
      editor.commit();
    }
}