java - "else"不工作

Question

public void randomFood (View view){
    Cursor mCursor = database.rawQuery("SELECT name FROM member ORDER BY RANDOM() LIMIT 1", null);
    if (mCursor != null) {
        mCursor.moveToFirst();
        String name = mCursor.getString(mCursor.getColumnIndex("name"));
        Log.i("===============", name);
        AlertDialog.Builder dialog = new AlertDialog.Builder(this);
        dialog.setTitle("This is your dog name");
        dialog.setCancelable(true);
        dialog.setMessage(name);
        dialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });
        dialog.show();
    }

    else{
        AlertDialog.Builder dialog = new AlertDialog.Builder(this);
        dialog.setTitle("Wait!!");
        dialog.setCancelable(true);
        dialog.setMessage("Please add information");
        dialog.setPositiveButton("Go", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                Intent intent = new Intent(Random.this, MainActivity.class);
                startActivity(intent);
            }
        });
        dialog.setNegativeButton("No", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                dialog.cancel();
            }
        });
        dialog.show();
    }
}

当我点击按钮时。如果数据库有信息(!mCursor.equals(null)or(mCursor != null)，它会随机并显示对话框。但是如果数据库没有信息...“else”不起作用.

不知道什么时候数据库没有信息，“mCursor”等于null？？？

Answer 1

这是因为总是返回一个非空值 - 甚至在您没有收到任何行的情况下(并且 SQL 不会抛出异常)

你最好重新编码你的 if

if(mCursor.getCount() > 0) {