Question

我正在构建一个使用按钮显示文本的应用程序，然后在某个时刻，相同的按钮将显示图像。

按钮以编程方式创建，具有不同的大小和位置。我使用了相对布局按钮。

我需要拖放按钮。我找到了一个管教程，向您展示如何制作可以拖放的文本视图。我完成了第一部分，可以让它拖动。我也让它适用于一个按钮。

当我将此代码添加到我的应用程序时 - 使用相对布局中的按钮它不起作用 - 应用程序崩溃。

下面是我的代码，我已经标记了导致应用程序崩溃的行。

package com.example.button;

import com.example.dragproject.MainActivity.DragShadow;

import android.os.Build;
import android.os.Bundle;
import android.annotation.TargetApi;
import android.app.Activity;
import android.content.ClipData;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Point;
import android.graphics.drawable.ColorDrawable;
import android.util.Log;
import android.view.DragEvent;
import android.view.Gravity;
import android.view.Menu;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnLongClickListener;
import android.view.View.OnTouchListener;
import android.view.ViewGroup;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;

public class MainActivity extends Activity {

    RelativeLayout layout;
    Button newButton;
    Button buttonByXml;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        buttonByXml = (Button)findViewById(R.id.button1);
        layout = (RelativeLayout)findViewById(R.id.RL);
        buttonByXml.setVisibility(View.GONE);

    button(500,300, (float) 230.2,(float) 230.2, 1, "untitled");
    button(200,400, (float) 430.2,(float) 630.2, 2, "untitled1");   

    button(250,150, (float) 130.2,(float) 730.2, 3, "untitled2");
    button(250,150, (float) 330.2,(float) 30.2, 3);
    }

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    public void button(int x, int y, float xx, float yy, int devno, String img) {

        String a = Integer.toString(devno);

        newButton = new Button(this);
        newButton.setOnLongClickListener((OnLongClickListener) this);//PROBLEM
        layout.addView(newButton);
        newButton.setX((float) xx);
        newButton.setY((float) yy);
        newButton.getLayoutParams().width = x;
        newButton.getLayoutParams().height = y;

        String mDrawableName = img;
        int resID = getResources().getIdentifier(mDrawableName , "drawable", getPackageName());

        newButton.setBackgroundResource(resID);

    }

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    public void button(int x, int y, float xx, float yy, int devno) {

        String a = Integer.toString(devno);

        newButton = new Button(this);
        newButton.setOnLongClickListener((OnLongClickListener) this);//PROBLEM
        layout.addView(newButton);
        newButton.setX((float) xx);
        newButton.setY((float) yy);
        newButton.getLayoutParams().width = x;
        newButton.getLayoutParams().height = y;

        newButton.setText(a);

    }


    OnLongClickListener Click = new OnLongClickListener(){

        @TargetApi(Build.VERSION_CODES.HONEYCOMB)
        @Override
        public boolean onLongClick(View v) {

            DragShadow dragshadow = new DragShadow(v);
            ClipData data = ClipData.newPlainText("", "");
            v.startDrag(data, dragshadow, v, 0);
            return false;

        }


    };

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    private class DragShadow extends View.DragShadowBuilder{

        ColorDrawable greyBox;

        public DragShadow(View view){
            super(view);
            greyBox = new ColorDrawable(Color.LTGRAY);
        }

        @Override
        public void onDrawShadow(Canvas canvas){
            greyBox.draw(canvas);
        }

        @TargetApi(Build.VERSION_CODES.HONEYCOMB)
        @Override
        public void onProvideShadowMetrics(Point shadowSize, Point shadowTouchPoint){

            View v = getView();
            int height = (int)v.getHeight();
            int width = (int)v.getWidth();
            greyBox.setBounds(0,0,width,height);
            shadowSize.set(width, height);
            shadowTouchPoint.set((int)width/2, (int)height/2);

        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

这是日志猫：

01-19 09:06:31.949: E/AndroidRuntime(19928): FATAL EXCEPTION: main
01-19 09:06:31.949: E/AndroidRuntime(19928): Process: com.example.button, PID: 19928
01-19 09:06:31.949: E/AndroidRuntime(19928): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.button/com.example.button.MainActivity}: java.lang.ClassCastException: com.example.button.MainActivity cannot be cast to android.view.View$OnLongClickListener
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.app.ActivityThread.access$700(ActivityThread.java:135)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.os.Handler.dispatchMessage(Handler.java:102)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.os.Looper.loop(Looper.java:137)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.app.ActivityThread.main(ActivityThread.java:4998)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at java.lang.reflect.Method.invokeNative(Native Method)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at java.lang.reflect.Method.invoke(Method.java:515)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at dalvik.system.NativeStart.main(Native Method)
01-19 09:06:31.949: E/AndroidRuntime(19928): Caused by: java.lang.ClassCastException: com.example.button.MainActivity cannot be cast to android.view.View$OnLongClickListener
01-19 09:06:31.949: E/AndroidRuntime(19928):    at com.example.button.MainActivity.button(MainActivity.java:57)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at com.example.button.MainActivity.onCreate(MainActivity.java:44)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.app.Activity.performCreate(Activity.java:5243)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-19 09:06:31.949: E/AndroidRuntime(19928):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
01-19 09:06:31.949: E/AndroidRuntime(19928):    ... 11 more

Answer 1

  newButton.setOnLongClickListener((OnLongClickListener) this);//PROBLEM

this是您的活动，而不是OnLongClickListener，转换失败。如果您的MainActivity implements onLongClickListener，它将起作用（即使没有演员表）。

您在此处初始化onLongClickListener：

 OnLongClickListener Click = new OnLongClickListener(){

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    @Override
    public boolean onLongClick(View v) {

        DragShadow dragshadow = new DragShadow(v);
        ClipData data = ClipData.newPlainText("", "");
        v.startDrag(data, dragshadow, v, 0);
        return false;

    }


};

所以使用它：

 newButton.setOnLongClickListener(Click);

为了样式，您应该将初始化移动到其他位置（类的开头，而不是在方法之间的中间）并使用小写名称。

Android拖放按钮相对布局

1 个答案: