问题描述
我想在布局的中心设置吐司的重力,但是当我添加重力并运行我的应用程序时,我的应用程序重新启动然后崩溃。我已经通过拿物体和不带物体两种方式尝试了吐司 这是我的代码。错误也附上
@Override
public void onBackpressed() {
new AlertDialog.Builder(MainActivity.this)
.setTitle("Exit")
.setIcon(R.drawable.ic_baseline_warning_24)
.setMessage("Sure? Your Want to Exit.")
.setPositiveButton("Yes",new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog,int which) {
finishAffinity();
}
}).setNegativeButton("No",new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog,int which) {
dialog.dismiss();
}
}).setNeutralButton("Other",int which) {
Toast toast = Toast.makeText(MainActivity.this,"Click yes for exit.",Toast.LENGTH_SHORT)
.setGravity(Gravity.CENTER,0);
toast.show();
}
}).show();
错误是从运行选项卡复制的
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.androiddevelopment,PID: 3210
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Toast.setGravity(int,int,int)' on a null object reference
at com.example.androiddevelopment.MainActivity$3.onClick(MainActivity.java:52)
at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:177)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
我也试过了,但问题没有解决
@Override
public void onBackpressed() {
new AlertDialog.Builder(MainActivity.this)
.setTitle("Exit")
.setIcon(R.drawable.ic_baseline_warning_24)
.setMessage("Are you sure you want to exit")
.setPositiveButton("yes",int which) {
finishAffinity();
}
}).setNeutralButton("Help","This is an \"Android Studio\" learning app",Toast.LENGTH_SHORT);
toast.setGravity(Gravity.CENTER,0);
toast.show();
}
}).setNegativeButton("No",int which) {
dialog.dismiss();
}
}).show();
}