[英]How do you pass values from an activity to a class in Android Studio?
我正在尝试设置删除按钮以从表中删除客户。 客户使用回收站视图显示在卡片视图中,因此每个客户都有自己的删除按钮。 客户信息使用文本视图显示。 我需要将客户 ID 传递给删除方法,以便在表中搜索要删除的特定 ID。 如何成功传递数据?
这就是我目前必须尝试传递我需要的数据
public void onBindViewHolder(@NonNull MyHolder holder, final int position) {
holder.idText.setText(String.valueOf(id.get(position)));
holder.nameText.setText(String.valueOf(name.get(position)));
holder.surnameText.setText(String.valueOf(surname.get(position)));
holder.add1Text.setText(String.valueOf(add1.get(position)));
holder.add2Text.setText(String.valueOf(add2.get(position)));
holder.add3Text.setText(String.valueOf(add3.get(position)));
holder.postCodeText.setText(String.valueOf(postCode.get(position)));
holder.phoneNumberText.setText(String.valueOf(phoneNumber.get(position)));
holder.emailText.setText(String.valueOf(email.get(position)));
GlobalVars.id = holder.idText.getText().toString();
holder.delete.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
db.deleteCustomer(GlobalVars.id);
}
});
}
这是我的删除方法:
public long deleteCustomer(String id)
{
SQLiteDatabase db = this.getWriteableDatabase();
ContentValues idValue = new ContentValues();
idValue.put(CUSTOMER_ID, id);
return db.delete(TABLE_NAME, "where Customer_ID = " + idValue, null);
}
当我运行该应用程序时,它会显示客户和按钮,但是当我单击任何按钮时,我会看到一个空白屏幕。 然后它返回到我的登录屏幕。
以下是LogCat中显示的错误:
2021-05-01 12:16:26.212 18729-18729/com.example.rowlandsflooringapp E/Zygote: isWhitelistProcess - Process is Whitelisted
2021-05-01 12:16:26.212 18729-18729/com.example.rowlandsflooringapp E/Zygote: accessInfo : 1
2021-05-01 12:16:26.244 18729-18729/com.example.rowlandsflooringapp E/andsflooringap: Unknown bits set in runtime_flags: 0x8000
2021-05-01 12:16:55.186 18729-18729/com.example.rowlandsflooringapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.rowlandsflooringapp, PID: 18729
java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.File android.content.Context.getDatabasePath(java.lang.String)' on a null object reference
at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:445)
at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:415)
at com.example.rowlandsflooringapp.CustomerDB.deleteCustomer(CustomerDB.java:70)
at com.example.rowlandsflooringapp.CustomerAdapter$1.onClick(CustomerAdapter.java:73)
at android.view.View.performClick(View.java:7862)
at android.widget.TextView.performClick(TextView.java:15004)
at android.view.View.performClickInternal(View.java:7831)
at android.view.View.access$3600(View.java:879)
at android.view.View$PerformClick.run(View.java:29359)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:237)
at android.app.ActivityThread.main(ActivityThread.java:8167)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:496)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1100)
经过几次尝试但都失败了,我决定再次从头开始创建删除方法。 这就是我最终得到的,而且效果很好。
数据库助手中的删除方法:
void deleteOneRow(String row_id){
SQLiteDatabase db = this.getWritableDatabase();
long result = db.delete(TABLE_NAME, "_id=?", new String[]{row_id});
if(result == -1){
Toast.makeText(context, "Failed to Delete.", Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(context, "Successfully Deleted.", Toast.LENGTH_SHORT).show();
}
调用删除方法:
void confirmDialog(){
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("Delete " + name + " ?");
builder.setMessage("Are you sure you want to delete " + name + " ?");
builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
MyDatabaseHelper myDB = new MyDatabaseHelper(UpdateActivity.this);
myDB.deleteOneRow(id);
finish();
}
});
builder.setNegativeButton("No", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialogInterface, int i) {
}
});
builder.create().show();
}
}
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