如何在子线程中查询数据库？

[qq_16545017]

SQLiteDatabase db = helper.getReadableDatabase();
Cursor cur = db.query("i", null, null, null, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Main.this, R.layout.list, cur, new String[]{"_id", "name", "favourite"}, new int[]{R.id.textView1, R.id.textView2, R.id.textView3}, 0);
ListView.setAdapter(adapter);

红米Note5Plus（RAM：4GB）可正常运行，
红米Note3（RAM：3GB）闪退。
已定位到问题出现在以上代码。

个人考虑是，读取（或查询）数据库可能比较费时，
需在线程中执行。
请问以上代码如何修改为在子线程中执行呢？不胜感激！

[r00_a2lBUR]

要在子线程查询数据库，前提是要会开一个子线程

[键盘舞者113]

   new Thread{
        @Override
        public void run() {
     SQLiteDatabase db = helper.getReadableDatabase();
Cursor cur = db.query("i", null, null, null, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Main.this, R.layout.list, cur, new String[]{"_id", "name", "favourite"}, new int[]{R.id.textView1, R.id.textView2, R.id.textView3}, 0);
ListView.setAdapter(adapter);
            
        }
    }.start();

[zhuailhw123]

开一个子线程

[qq_16545017]

引用 2 楼 z979451341 的回复:

   new Thread{
        @Override
        public void run() {
     SQLiteDatabase db = helper.getReadableDatabase();
Cursor cur = db.query("i", null, null, null, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Main.this, R.layout.list, cur, new String[]{"_id", "name", "favourite"}, new int[]{R.id.textView1, R.id.textView2, R.id.textView3}, 0);
ListView.setAdapter(adapter);
            
        }
    }.start();

子线程不能更新UI线程控件，ANR……

[键盘舞者113]

引用 4 楼 qq_16545017 的回复:

[quote=引用 2 楼 z979451341 的回复:]

   new Thread{
        @Override
        public void run() {
     SQLiteDatabase db = helper.getReadableDatabase();
Cursor cur = db.query("i", null, null, null, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Main.this, R.layout.list, cur, new String[]{"_id", "name", "favourite"}, new int[]{R.id.textView1, R.id.textView2, R.id.textView3}, 0);
ListView.setAdapter(adapter);
            
        }
    }.start();

子线程不能更新UI线程控件，ANR……[/quote]
Handler通知一下就行了

[键盘舞者113]

大兄弟，你去把《疯狂学Android 》 ，《第一行代码》都看一下，demo照着打一下，基础必须学好，要不然以后问题很多

[qq_16545017]

引用 5 楼 z979451341 的回复:

[quote=引用 4 楼 qq_16545017 的回复:]
[quote=引用 2 楼 z979451341 的回复:]

   new Thread{
        @Override
        public void run() {
     SQLiteDatabase db = helper.getReadableDatabase();
Cursor cur = db.query("i", null, null, null, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Main.this, R.layout.list, cur, new String[]{"_id", "name", "favourite"}, new int[]{R.id.textView1, R.id.textView2, R.id.textView3}, 0);
ListView.setAdapter(adapter);
            
        }
    }.start();

子线程不能更新UI线程控件，ANR……[/quote]
Handler通知一下就行了[/quote]

请问如何用Handler通知啊？谢谢！

[雕·不懒惰]

private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
if(msg.what==0x110）{
ListView.setAdapter(adapter);
}
}
};

new Thread{
@Override
public void run() {
SQLiteDatabase db = helper.getReadableDatabase();
Cursor cur = db.query("i", null, null, null, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Main.this, R.layout.list, cur, new String[]{"_id", "name", "favourite"}, new int[]{R.id.textView1, R.id.textView2, R.id.textView3}, 0);
handler.sendEmptyMessage(0x110);
}
}.start();

[qq_16545017]

引用 9 楼 qq_33451426 的回复:

private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
if(msg.what==0x110）{
ListView.setAdapter(adapter);
}
}
};

new Thread{
@Override
public void run() {
SQLiteDatabase db = helper.getReadableDatabase();
Cursor cur = db.query("i", null, null, null, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Main.this, R.layout.list, cur, new String[]{"_id", "name", "favourite"}, new int[]{R.id.textView1, R.id.textView2, R.id.textView3}, 0);
handler.sendEmptyMessage(0x110);
}
}.start();

The local variable adapter may not have been initialized

[Krisez]

创建一个handler
子线程更新数据完后
handler.sendMessage 通知然后handler里的方法进行操作数据ui

[雕·不懒惰]

引用 10 楼 qq_16545017 的回复:

[quote=引用 9 楼 qq_33451426 的回复:]
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
if(msg.what==0x110）{
ListView.setAdapter(adapter);
}
}
};

new Thread{
@Override
public void run() {
SQLiteDatabase db = helper.getReadableDatabase();
Cursor cur = db.query("i", null, null, null, null, null, null);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(Main.this, R.layout.list, cur, new String[]{"_id", "name", "favourite"}, new int[]{R.id.textView1, R.id.textView2, R.id.textView3}, 0);
handler.sendEmptyMessage(0x110);
}
}.start();

The local variable adapter may not have been initialized[/quote]

大哥 adapter没初始化啊，这你都不知道，你得把adapter定义全局的