当我启动我的应用程序时,它会崩溃并给出错误代码。
尝试对空对象引用调用虚拟方法“android.content.sharedpreferences android.content.context.getsharedpreferences(java.lang.string,int)”。
这对我来说很新鲜,请帮帮我。
这是我的主要活动
package com.awplicity.testappshared;
import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
SharedPreferences sharedPreferences = getSharedPreferences("", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
Button button1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
private void onClick(View v) {
switch(v.getId()) {
case R.id.nextAct:
editor.putString("mystring", "Hi");
editor.commit();
startActivity(new Intent("com.awplicity.testappshared.Main2Activity"));
break;
}
}
}
这是第二个活动
package com.awplicity.testappshared;
import android.content.Context;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
public class Main2Activity extends AppCompatActivity {
TextView tv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main2);
tv = (TextView) findViewById(R.id.tv_main2);
setText();
}
public void setText() {
SharedPreferences sharedPreferences = getSharedPreferences("", Context.MODE_PRIVATE);
tv.setText(sharedPreferences.getString("mystring", ""));
}
}
最佳答案
一般来说,除非在Activity
方法内部,否则不能调用从AppCompatActivity
继承的方法(或子类,如onCreate()
)。在那之前,事情还没有准备好。
因此,改变:
SharedPreferences sharedPreferences = getSharedPreferences("", Context.MODE_PRIVATE);
SharedPreferences.Editor editor = sharedPreferences.edit();
到:
SharedPreferences sharedPreferences;
SharedPreferences.Editor editor;
并在
onCreate()
中初始化这些字段:@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
sharedPreferences = getSharedPreferences("", Context.MODE_PRIVATE);
editor = sharedPreferences.edit();
}